// This is an open source non-commercial project. Dear PVS-Studio, please check
// it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com

// for debugging
// #define CHECK(c, s) do { if (c) emsg(s); } while (0)
#define CHECK(c, s) do { } while (0)

/*
 * memline.c: Contains the functions for appending, deleting and changing the
 * text lines. The memfile functions are used to store the information in
 * blocks of memory, backed up by a file. The structure of the information is
 * a tree.  The root of the tree is a pointer block. The leaves of the tree
 * are data blocks. In between may be several layers of pointer blocks,
 * forming branches.
 *
 * Three types of blocks are used:
 * - Block nr 0 contains information for recovery
 * - Pointer blocks contain list of pointers to other blocks.
 * - Data blocks contain the actual text.
 *
 * Block nr 0 contains the block0 structure (see below).
 *
 * Block nr 1 is the first pointer block. It is the root of the tree.
 * Other pointer blocks are branches.
 *
 *  If a line is too big to fit in a single page, the block containing that
 *  line is made big enough to hold the line. It may span several pages.
 *  Otherwise all blocks are one page.
 *
 *  A data block that was filled when starting to edit a file and was not
 *  changed since then, can have a negative block number. This means that it
 *  has not yet been assigned a place in the file. When recovering, the lines
 *  in this data block can be read from the original file. When the block is
 *  changed (lines appended/deleted/changed) or when it is flushed it gets a
 *  positive number. Use mf_trans_del() to get the new number, before calling
 *  mf_get().
 */

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdbool.h>
#include <string.h>

#include "nvim/ascii.h"
#include "nvim/buffer.h"
#include "nvim/change.h"
#include "nvim/cursor.h"
#include "nvim/eval.h"
#include "nvim/fileio.h"
#include "nvim/func_attr.h"
#include "nvim/getchar.h"
#include "nvim/main.h"
#include "nvim/mark.h"
#include "nvim/mbyte.h"
#include "nvim/memfile.h"
#include "nvim/memline.h"
#include "nvim/memory.h"
#include "nvim/message.h"
#include "nvim/misc1.h"
#include "nvim/option.h"
#include "nvim/os/input.h"
#include "nvim/os/os.h"
#include "nvim/os/process.h"
#include "nvim/os_unix.h"
#include "nvim/path.h"
#include "nvim/screen.h"
#include "nvim/sha256.h"
#include "nvim/spell.h"
#include "nvim/strings.h"
#include "nvim/ui.h"
#include "nvim/undo.h"
#include "nvim/version.h"
#include "nvim/vim.h"
#include "nvim/window.h"

#ifndef UNIX            // it's in os/unix_defs.h for Unix
# include <time.h>
#endif

typedef struct block0 ZERO_BL;              // contents of the first block
typedef struct pointer_block PTR_BL;        // contents of a pointer block
typedef struct data_block DATA_BL;          // contents of a data block
typedef struct pointer_entry PTR_EN;        // block/line-count pair

#define DATA_ID        (('d' << 8) + 'a')   // data block id
#define PTR_ID         (('p' << 8) + 't')   // pointer block id
#define BLOCK0_ID0     'b'                  // block 0 id 0
#define BLOCK0_ID1     '0'                  // block 0 id 1

/*
 * pointer to a block, used in a pointer block
 */
struct pointer_entry {
  blocknr_T pe_bnum;            // block number
  linenr_T pe_line_count;       // number of lines in this branch
  linenr_T pe_old_lnum;         // lnum for this block (for recovery)
  int pe_page_count;            // number of pages in block pe_bnum
};

/*
 * A pointer block contains a list of branches in the tree.
 */
struct pointer_block {
  uint16_t pb_id;               // ID for pointer block: PTR_ID
  uint16_t pb_count;            // number of pointers in this block
  uint16_t pb_count_max;        // maximum value for pb_count
  PTR_EN pb_pointer[1];         // list of pointers to blocks (actually longer)
                                // followed by empty space until end of page
};

/*
 * A data block is a leaf in the tree.
 *
 * The text of the lines is at the end of the block. The text of the first line
 * in the block is put at the end, the text of the second line in front of it,
 * etc. Thus the order of the lines is the opposite of the line number.
 */
struct data_block {
  uint16_t db_id;               // ID for data block: DATA_ID
  unsigned db_free;             // free space available
  unsigned db_txt_start;        // byte where text starts
  unsigned db_txt_end;          // byte just after data block
  linenr_T db_line_count;       // number of lines in this block
  unsigned db_index[1];         // index for start of line (actually bigger)
                                // followed by empty space up to db_txt_start
                                // followed by the text in the lines until
                                // end of page
};

/*
 * The low bits of db_index hold the actual index. The topmost bit is
 * used for the global command to be able to mark a line.
 * This method is not clean, but otherwise there would be at least one extra
 * byte used for each line.
 * The mark has to be in this place to keep it with the correct line when other
 * lines are inserted or deleted.
 */
#define DB_MARKED       ((unsigned)1 << ((sizeof(unsigned) * 8) - 1))
#define DB_INDEX_MASK   (~DB_MARKED)

#define INDEX_SIZE  (sizeof(unsigned))      // size of one db_index entry
#define HEADER_SIZE (sizeof(DATA_BL) - INDEX_SIZE)  // size of data block header

#define B0_FNAME_SIZE_ORG       900     // what it was in older versions
#define B0_FNAME_SIZE_NOCRYPT   898     // 2 bytes used for other things
#define B0_FNAME_SIZE_CRYPT     890     // 10 bytes used for other things
#define B0_UNAME_SIZE           40
#define B0_HNAME_SIZE           40
/*
 * Restrict the numbers to 32 bits, otherwise most compilers will complain.
 * This won't detect a 64 bit machine that only swaps a byte in the top 32
 * bits, but that is crazy anyway.
 */
#define B0_MAGIC_LONG   0x30313233L
#define B0_MAGIC_INT    0x20212223L
#define B0_MAGIC_SHORT  0x10111213L
#define B0_MAGIC_CHAR   0x55

/*
 * Block zero holds all info about the swap file.
 *
 * NOTE: DEFINITION OF BLOCK 0 SHOULD NOT CHANGE! It would make all existing
 * swap files unusable!
 *
 * If size of block0 changes anyway, adjust MIN_SWAP_PAGE_SIZE in vim.h!!
 *
 * This block is built up of single bytes, to make it portable across
 * different machines. b0_magic_* is used to check the byte order and size of
 * variables, because the rest of the swap file is not portable.
 */
struct block0 {
  char_u b0_id[2];              ///< ID for block 0: BLOCK0_ID0 and BLOCK0_ID1.
  char_u b0_version[10];        // Vim version string
  char_u b0_page_size[4];       // number of bytes per page
  char_u b0_mtime[4];           // last modification time of file
  char_u b0_ino[4];             // inode of b0_fname
  char_u b0_pid[4];             // process id of creator (or 0)
  char_u b0_uname[B0_UNAME_SIZE];        // name of user (uid if no name)
  char_u b0_hname[B0_HNAME_SIZE];        // host name (if it has a name)
  char_u b0_fname[B0_FNAME_SIZE_ORG];        // name of file being edited
  long b0_magic_long;           // check for byte order of long
  int b0_magic_int;             // check for byte order of int
  short b0_magic_short;         // check for byte order of short
  char_u b0_magic_char;         // check for last char
};

/*
 * Note: b0_dirty and b0_flags are put at the end of the file name.  For very
 * long file names in older versions of Vim they are invalid.
 * The 'fileencoding' comes before b0_flags, with a NUL in front.  But only
 * when there is room, for very long file names it's omitted.
 */
#define B0_DIRTY        0x55
#define b0_dirty        b0_fname[B0_FNAME_SIZE_ORG - 1]

/*
 * The b0_flags field is new in Vim 7.0.
 */
#define b0_flags        b0_fname[B0_FNAME_SIZE_ORG - 2]

// The lowest two bits contain the fileformat.  Zero means it's not set
// (compatible with Vim 6.x), otherwise it's EOL_UNIX + 1, EOL_DOS + 1 or
// EOL_MAC + 1.
#define B0_FF_MASK      3

// Swap file is in directory of edited file.  Used to find the file from
// different mount points.
#define B0_SAME_DIR     4

// The 'fileencoding' is at the end of b0_fname[], with a NUL in front of it.
// When empty there is only the NUL.
#define B0_HAS_FENC     8

#define STACK_INCR      5       // nr of entries added to ml_stack at a time

/*
 * The line number where the first mark may be is remembered.
 * If it is 0 there are no marks at all.
 * (always used for the current buffer only, no buffer change possible while
 * executing a global command).
 */
static linenr_T lowest_marked = 0;

/*
 * arguments for ml_find_line()
 */
#define ML_DELETE       0x11        // delete line
#define ML_INSERT       0x12        // insert line
#define ML_FIND         0x13        // just find the line
#define ML_FLUSH        0x02        // flush locked block
#define ML_SIMPLE(x)    (x & 0x10)  // DEL, INS or FIND

// argument for ml_upd_block0()
typedef enum {
  UB_FNAME = 0,         // update timestamp and filename
  UB_SAME_DIR,  // update the B0_SAME_DIR flag
} upd_block0_T;

#ifdef INCLUDE_GENERATED_DECLARATIONS
# include "memline.c.generated.h"
#endif

/*
 * Open a new memline for "buf".
 *
 * Return FAIL for failure, OK otherwise.
 */
int ml_open(buf_T *buf)
{
  bhdr_T *hp = NULL;
  ZERO_BL *b0p;
  PTR_BL *pp;
  DATA_BL *dp;

  /*
   * init fields in memline struct
   */
  buf->b_ml.ml_stack_size = 0;   // no stack yet
  buf->b_ml.ml_stack = NULL;    // no stack yet
  buf->b_ml.ml_stack_top = 0;   // nothing in the stack
  buf->b_ml.ml_locked = NULL;   // no cached block
  buf->b_ml.ml_line_lnum = 0;   // no cached line
  buf->b_ml.ml_line_offset = 0;
  buf->b_ml.ml_chunksize = NULL;
  buf->b_ml.ml_usedchunks = 0;

  if (cmdmod.noswapfile) {
    buf->b_p_swf = false;
  }

  /*
   * When 'updatecount' is non-zero swap file may be opened later.
   */
  if (!buf->terminal && p_uc && buf->b_p_swf) {
    buf->b_may_swap = true;
  } else {
    buf->b_may_swap = false;
  }

  // Open the memfile.  No swap file is created yet.
  memfile_T *mfp = mf_open(NULL, 0);
  if (mfp == NULL) {
    goto error;
  }

  buf->b_ml.ml_mfp = mfp;
  buf->b_ml.ml_flags = ML_EMPTY;
  buf->b_ml.ml_line_count = 1;
  curwin->w_nrwidth_line_count = 0;


  /*
   * fill block0 struct and write page 0
   */
  hp = mf_new(mfp, false, 1);
  if (hp->bh_bnum != 0) {
    iemsg(_("E298: Didn't get block nr 0?"));
    goto error;
  }
  b0p = hp->bh_data;

  b0p->b0_id[0] = BLOCK0_ID0;
  b0p->b0_id[1] = BLOCK0_ID1;
  b0p->b0_magic_long = (long)B0_MAGIC_LONG;
  b0p->b0_magic_int = (int)B0_MAGIC_INT;
  b0p->b0_magic_short = (short)B0_MAGIC_SHORT;
  b0p->b0_magic_char = B0_MAGIC_CHAR;
  xstrlcpy(xstpcpy((char *)b0p->b0_version, "VIM "), Version, 6);
  long_to_char((long)mfp->mf_page_size, b0p->b0_page_size);

  if (!buf->b_spell) {
    b0p->b0_dirty = buf->b_changed ? B0_DIRTY : 0;
    b0p->b0_flags = get_fileformat(buf) + 1;
    set_b0_fname(b0p, buf);
    (void)os_get_user_name((char *)b0p->b0_uname, B0_UNAME_SIZE);
    b0p->b0_uname[B0_UNAME_SIZE - 1] = NUL;
    os_get_hostname((char *)b0p->b0_hname, B0_HNAME_SIZE);
    b0p->b0_hname[B0_HNAME_SIZE - 1] = NUL;
    long_to_char(os_get_pid(), b0p->b0_pid);
  }

  /*
   * Always sync block number 0 to disk, so we can check the file name in
   * the swap file in findswapname(). Don't do this for a help files or
   * a spell buffer though.
   * Only works when there's a swapfile, otherwise it's done when the file
   * is created.
   */
  mf_put(mfp, hp, true, false);
  if (!buf->b_help && !B_SPELL(buf)) {
    (void)mf_sync(mfp, 0);
  }

  /*
   * Fill in root pointer block and write page 1.
   */
  if ((hp = ml_new_ptr(mfp)) == NULL) {
    goto error;
  }
  if (hp->bh_bnum != 1) {
    iemsg(_("E298: Didn't get block nr 1?"));
    goto error;
  }
  pp = hp->bh_data;
  pp->pb_count = 1;
  pp->pb_pointer[0].pe_bnum = 2;
  pp->pb_pointer[0].pe_page_count = 1;
  pp->pb_pointer[0].pe_old_lnum = 1;
  pp->pb_pointer[0].pe_line_count = 1;      // line count after insertion
  mf_put(mfp, hp, true, false);

  /*
   * Allocate first data block and create an empty line 1.
   */
  hp = ml_new_data(mfp, false, 1);
  if (hp->bh_bnum != 2) {
    iemsg(_("E298: Didn't get block nr 2?"));
    goto error;
  }

  dp = hp->bh_data;
  dp->db_index[0] = --dp->db_txt_start;         // at end of block
  dp->db_free -= 1 + INDEX_SIZE;
  dp->db_line_count = 1;
  *((char_u *)dp + dp->db_txt_start) = NUL;     // empty line

  return OK;

error:
  if (mfp != NULL) {
    if (hp) {
      mf_put(mfp, hp, false, false);
    }
    mf_close(mfp, true);  // will also xfree(mfp->mf_fname)
  }
  buf->b_ml.ml_mfp = NULL;
  return FAIL;
}

/*
 * ml_setname() is called when the file name of "buf" has been changed.
 * It may rename the swap file.
 */
void ml_setname(buf_T *buf)
{
  bool success = false;
  memfile_T *mfp;
  char_u *fname;
  char_u *dirp;

  mfp = buf->b_ml.ml_mfp;
  if (mfp->mf_fd < 0) {             // there is no swap file yet
    /*
     * When 'updatecount' is 0 and 'noswapfile' there is no swap file.
     * For help files we will make a swap file now.
     */
    if (p_uc != 0 && !cmdmod.noswapfile) {
      ml_open_file(buf);  // create a swap file
    }
    return;
  }

  /*
   * Try all directories in the 'directory' option.
   */
  dirp = p_dir;
  bool found_existing_dir = false;
  for (;;) {
    if (*dirp == NUL) {             // tried all directories, fail
      break;
    }
    fname = (char_u *)findswapname(buf, (char **)&dirp, (char *)mfp->mf_fname,
                                   &found_existing_dir);
    // alloc's fname
    if (dirp == NULL) {             // out of memory
      break;
    }
    if (fname == NULL) {            // no file name found for this dir
      continue;
    }

    // if the file name is the same we don't have to do anything
    if (fnamecmp(fname, mfp->mf_fname) == 0) {
      xfree(fname);
      success = true;
      break;
    }
    // need to close the swap file before renaming
    if (mfp->mf_fd >= 0) {
      close(mfp->mf_fd);
      mfp->mf_fd = -1;
    }

    // try to rename the swap file
    if (vim_rename(mfp->mf_fname, fname) == 0) {
      success = true;
      mf_free_fnames(mfp);
      mf_set_fnames(mfp, fname);
      ml_upd_block0(buf, UB_SAME_DIR);
      break;
    }
    xfree(fname);                // this fname didn't work, try another
  }

  if (mfp->mf_fd == -1) {           // need to (re)open the swap file
    mfp->mf_fd = os_open((char *)mfp->mf_fname, O_RDWR, 0);
    if (mfp->mf_fd < 0) {
      // could not (re)open the swap file, what can we do????
      emsg(_("E301: Oops, lost the swap file!!!"));
      return;
    }
    (void)os_set_cloexec(mfp->mf_fd);
  }
  if (!success) {
    emsg(_("E302: Could not rename swap file"));
  }
}

/*
 * Open a file for the memfile for all buffers that are not readonly or have
 * been modified.
 * Used when 'updatecount' changes from zero to non-zero.
 */
void ml_open_files(void)
{
  FOR_ALL_BUFFERS(buf) {
    if (!buf->b_p_ro || buf->b_changed) {
      ml_open_file(buf);
    }
  }
}

/*
 * Open a swap file for an existing memfile, if there is no swap file yet.
 * If we are unable to find a file name, mf_fname will be NULL
 * and the memfile will be in memory only (no recovery possible).
 */
void ml_open_file(buf_T *buf)
{
  memfile_T *mfp;
  char_u *fname;
  char_u *dirp;

  mfp = buf->b_ml.ml_mfp;
  if (mfp == NULL || mfp->mf_fd >= 0 || !buf->b_p_swf || cmdmod.noswapfile
      || buf->terminal) {
    return;  // nothing to do
  }

  // For a spell buffer use a temp file name.
  if (buf->b_spell) {
    fname = vim_tempname();
    if (fname != NULL) {
      (void)mf_open_file(mfp, fname);           // consumes fname!
    }
    buf->b_may_swap = false;
    return;
  }

  /*
   * Try all directories in 'directory' option.
   */
  dirp = p_dir;
  bool found_existing_dir = false;
  for (;;) {
    if (*dirp == NUL) {
      break;
    }
    // There is a small chance that between choosing the swap file name
    // and creating it, another Vim creates the file.  In that case the
    // creation will fail and we will use another directory.
    fname = (char_u *)findswapname(buf, (char **)&dirp, NULL,
                                   &found_existing_dir);
    if (dirp == NULL) {
      break;        // out of memory
    }
    if (fname == NULL) {
      continue;
    }
    if (mf_open_file(mfp, fname) == OK) {       // consumes fname!
      ml_upd_block0(buf, UB_SAME_DIR);

      // Flush block zero, so others can read it
      if (mf_sync(mfp, MFS_ZERO) == OK) {
        // Mark all blocks that should be in the swapfile as dirty.
        // Needed for when the 'swapfile' option was reset, so that
        // the swap file was deleted, and then on again.
        mf_set_dirty(mfp);
        break;
      }
      // Writing block 0 failed: close the file and try another dir
      mf_close_file(buf, false);
    }
  }

  if (*p_dir != NUL && mfp->mf_fname == NULL) {
    need_wait_return = true;  // call wait_return later
    no_wait_return++;
    (void)semsg(_("E303: Unable to open swap file for \"%s\", recovery impossible"),
                buf_spname(buf) != NULL ? buf_spname(buf) : buf->b_fname);
    --no_wait_return;
  }

  // don't try to open a swap file again
  buf->b_may_swap = false;
}

/// If still need to create a swap file, and starting to edit a not-readonly
/// file, or reading into an existing buffer, create a swap file now.
///
/// @param newfile reading file into new buffer
void check_need_swap(bool newfile)
{
  int old_msg_silent = msg_silent;  // might be reset by an E325 message
  msg_silent = 0;  // If swap dialog prompts for input, user needs to see it!

  if (curbuf->b_may_swap && (!curbuf->b_p_ro || !newfile)) {
    ml_open_file(curbuf);
  }

  msg_silent = old_msg_silent;
}

/*
 * Close memline for buffer 'buf'.
 * If 'del_file' is TRUE, delete the swap file
 */
void ml_close(buf_T *buf, int del_file)
{
  if (buf->b_ml.ml_mfp == NULL) {               // not open
    return;
  }
  mf_close(buf->b_ml.ml_mfp, del_file);       // close the .swp file
  if (buf->b_ml.ml_line_lnum != 0 && (buf->b_ml.ml_flags & ML_LINE_DIRTY)) {
    xfree(buf->b_ml.ml_line_ptr);
  }
  xfree(buf->b_ml.ml_stack);
  XFREE_CLEAR(buf->b_ml.ml_chunksize);
  buf->b_ml.ml_mfp = NULL;

  // Reset the "recovered" flag, give the ATTENTION prompt the next time
  // this buffer is loaded.
  buf->b_flags &= ~BF_RECOVERED;
}

/*
 * Close all existing memlines and memfiles.
 * Only used when exiting.
 * When 'del_file' is TRUE, delete the memfiles.
 * But don't delete files that were ":preserve"d when we are POSIX compatible.
 */
void ml_close_all(int del_file)
{
  FOR_ALL_BUFFERS(buf) {
    ml_close(buf, del_file && ((buf->b_flags & BF_PRESERVED) == 0));
  }
  spell_delete_wordlist();      // delete the internal wordlist
  vim_deltempdir();             // delete created temp directory
}

/*
 * Close all memfiles for not modified buffers.
 * Only use just before exiting!
 */
void ml_close_notmod(void)
{
  FOR_ALL_BUFFERS(buf) {
    if (!bufIsChanged(buf)) {
      ml_close(buf, TRUE);          // close all not-modified buffers
    }
  }
}

/*
 * Update the timestamp in the .swp file.
 * Used when the file has been written.
 */
void ml_timestamp(buf_T *buf)
{
  ml_upd_block0(buf, UB_FNAME);
}

/// Checks whether the IDs in b0 are valid.
static bool ml_check_b0_id(ZERO_BL *b0p)
  FUNC_ATTR_NONNULL_ALL
{
  return b0p->b0_id[0] == BLOCK0_ID0 && b0p->b0_id[1] == BLOCK0_ID1;
}

/// Checks whether all strings in b0 are valid (i.e. nul-terminated).
static bool ml_check_b0_strings(ZERO_BL *b0p)
  FUNC_ATTR_NONNULL_ALL
{
  return (memchr(b0p->b0_version, NUL, 10)
          && memchr(b0p->b0_uname, NUL, B0_UNAME_SIZE)
          && memchr(b0p->b0_hname, NUL, B0_HNAME_SIZE)
          && memchr(b0p->b0_fname, NUL, B0_FNAME_SIZE_CRYPT));  // -V512
}

/*
 * Update the timestamp or the B0_SAME_DIR flag of the .swp file.
 */
static void ml_upd_block0(buf_T *buf, upd_block0_T what)
{
  memfile_T *mfp;
  bhdr_T *hp;
  ZERO_BL *b0p;

  mfp = buf->b_ml.ml_mfp;
  if (mfp == NULL || (hp = mf_get(mfp, 0, 1)) == NULL) {
    return;
  }
  b0p = hp->bh_data;
  if (ml_check_b0_id(b0p) == FAIL) {
    iemsg(_("E304: ml_upd_block0(): Didn't get block 0??"));
  } else {
    if (what == UB_FNAME) {
      set_b0_fname(b0p, buf);
    } else {    // what == UB_SAME_DIR
      set_b0_dir_flag(b0p, buf);
    }
  }
  mf_put(mfp, hp, true, false);
}

/*
 * Write file name and timestamp into block 0 of a swap file.
 * Also set buf->b_mtime.
 * Don't use NameBuff[]!!!
 */
static void set_b0_fname(ZERO_BL *b0p, buf_T *buf)
{
  if (buf->b_ffname == NULL) {
    b0p->b0_fname[0] = NUL;
  } else {
    char uname[B0_UNAME_SIZE];

    /*
     * For a file under the home directory of the current user, we try to
     * replace the home directory path with "~user". This helps when
     * editing the same file on different machines over a network.
     * First replace home dir path with "~/" with home_replace().
     * Then insert the user name to get "~user/".
     */
    home_replace(NULL, buf->b_ffname, b0p->b0_fname,
                 B0_FNAME_SIZE_CRYPT, TRUE);
    if (b0p->b0_fname[0] == '~') {
      // If there is no user name or it is too long, don't use "~/"
      int retval = os_get_user_name(uname, B0_UNAME_SIZE);
      size_t ulen = STRLEN(uname);
      size_t flen = STRLEN(b0p->b0_fname);
      if (retval == FAIL || ulen + flen > B0_FNAME_SIZE_CRYPT - 1) {
        STRLCPY(b0p->b0_fname, buf->b_ffname, B0_FNAME_SIZE_CRYPT);
      } else {
        memmove(b0p->b0_fname + ulen + 1, b0p->b0_fname + 1, flen);
        memmove(b0p->b0_fname + 1, uname, ulen);
      }
    }
    FileInfo file_info;
    if (os_fileinfo((char *)buf->b_ffname, &file_info)) {
      long_to_char(file_info.stat.st_mtim.tv_sec, b0p->b0_mtime);
      long_to_char((long)os_fileinfo_inode(&file_info), b0p->b0_ino);
      buf_store_file_info(buf, &file_info);
      buf->b_mtime_read = buf->b_mtime;
    } else {
      long_to_char(0L, b0p->b0_mtime);
      long_to_char(0L, b0p->b0_ino);
      buf->b_mtime = 0;
      buf->b_mtime_read = 0;
      buf->b_orig_size = 0;
      buf->b_orig_mode = 0;
    }
  }

  // Also add the 'fileencoding' if there is room.
  add_b0_fenc(b0p, curbuf);
}

/*
 * Update the B0_SAME_DIR flag of the swap file.  It's set if the file and the
 * swapfile for "buf" are in the same directory.
 * This is fail safe: if we are not sure the directories are equal the flag is
 * not set.
 */
static void set_b0_dir_flag(ZERO_BL *b0p, buf_T *buf)
{
  if (same_directory(buf->b_ml.ml_mfp->mf_fname, buf->b_ffname)) {
    b0p->b0_flags |= B0_SAME_DIR;
  } else {
    b0p->b0_flags &= ~B0_SAME_DIR;
  }
}

/*
 * When there is room, add the 'fileencoding' to block zero.
 */
static void add_b0_fenc(ZERO_BL *b0p, buf_T *buf)
{
  int n;
  int size = B0_FNAME_SIZE_NOCRYPT;

  n = (int)STRLEN(buf->b_p_fenc);
  if ((int)STRLEN(b0p->b0_fname) + n + 1 > size) {
    b0p->b0_flags &= ~B0_HAS_FENC;
  } else {
    memmove((char *)b0p->b0_fname + size - n,
            (char *)buf->b_p_fenc, (size_t)n);
    *(b0p->b0_fname + size - n - 1) = NUL;
    b0p->b0_flags |= B0_HAS_FENC;
  }
}


/// Try to recover curbuf from the .swp file.
/// @param checkext If true, check the extension and detect whether it is a
/// swap file.
void ml_recover(bool checkext)
{
  buf_T *buf = NULL;
  memfile_T *mfp = NULL;
  char_u *fname;
  char_u *fname_used = NULL;
  bhdr_T *hp = NULL;
  ZERO_BL *b0p;
  int b0_ff;
  char_u *b0_fenc = NULL;
  PTR_BL *pp;
  DATA_BL *dp;
  infoptr_T *ip;
  blocknr_T bnum;
  int page_count;
  int len;
  bool directly;
  linenr_T lnum;
  char_u *p;
  int i;
  long error;
  bool cannot_open;
  linenr_T line_count;
  bool has_error;
  int idx;
  int top;
  int txt_start;
  off_T size;
  int called_from_main;
  bool serious_error = true;
  long mtime;
  int attr;
  int orig_file_status = NOTDONE;

  recoverymode = TRUE;
  called_from_main = (curbuf->b_ml.ml_mfp == NULL);
  attr = HL_ATTR(HLF_E);

  // If the file name ends in ".s[a-w][a-z]" we assume this is the swap file.
  // Otherwise a search is done to find the swap file(s).
  fname = curbuf->b_fname;
  if (fname == NULL) {              // When there is no file name
    fname = (char_u *)"";
  }
  len = (int)STRLEN(fname);
  if (checkext && len >= 4
      && STRNICMP(fname + len - 4, ".s", 2) == 0
      && vim_strchr((char_u *)"abcdefghijklmnopqrstuvw",
                    TOLOWER_ASC(fname[len - 2])) != NULL
      && ASCII_ISALPHA(fname[len - 1])) {
    directly = true;
    fname_used = vim_strsave(fname);     // make a copy for mf_open()
  } else {
    directly = false;

    // count the number of matching swap files
    len = recover_names(fname, FALSE, 0, NULL);
    if (len == 0) {                 // no swap files found
      semsg(_("E305: No swap file found for %s"), fname);
      goto theend;
    }
    if (len == 1) {                 // one swap file found, use it
      i = 1;
    } else {                          // several swap files found, choose
      // list the names of the swap files
      (void)recover_names(fname, TRUE, 0, NULL);
      msg_putchar('\n');
      msg_puts(_("Enter number of swap file to use (0 to quit): "));
      i = get_number(FALSE, NULL);
      if (i < 1 || i > len) {
        goto theend;
      }
    }
    // get the swap file name that will be used
    (void)recover_names(fname, FALSE, i, &fname_used);
  }
  if (fname_used == NULL) {
    goto theend;  // user chose invalid number.
  }
  // When called from main() still need to initialize storage structure
  if (called_from_main && ml_open(curbuf) == FAIL) {
    getout(1);
  }

  /*
   * Allocate a buffer structure for the swap file that is used for recovery.
   * Only the memline in it is really used.
   */
  buf = xmalloc(sizeof(buf_T));

  /*
   * init fields in memline struct
   */
  buf->b_ml.ml_stack_size = 0;          // no stack yet
  buf->b_ml.ml_stack = NULL;            // no stack yet
  buf->b_ml.ml_stack_top = 0;           // nothing in the stack
  buf->b_ml.ml_line_lnum = 0;           // no cached line
  buf->b_ml.ml_line_offset = 0;
  buf->b_ml.ml_locked = NULL;           // no locked block
  buf->b_ml.ml_flags = 0;

  /*
   * open the memfile from the old swap file
   */
  p = vim_strsave(fname_used);  // save "fname_used" for the message:
                                // mf_open() will consume "fname_used"!
  mfp = mf_open(fname_used, O_RDONLY);
  fname_used = p;
  if (mfp == NULL || mfp->mf_fd < 0) {
    semsg(_("E306: Cannot open %s"), fname_used);
    goto theend;
  }
  buf->b_ml.ml_mfp = mfp;

  /*
   * The page size set in mf_open() might be different from the page size
   * used in the swap file, we must get it from block 0.  But to read block
   * 0 we need a page size.  Use the minimal size for block 0 here, it will
   * be set to the real value below.
   */
  mfp->mf_page_size = MIN_SWAP_PAGE_SIZE;

  /*
   * try to read block 0
   */
  if ((hp = mf_get(mfp, 0, 1)) == NULL) {
    msg_start();
    msg_puts_attr(_("Unable to read block 0 from "), attr | MSG_HIST);
    msg_outtrans_attr(mfp->mf_fname, attr | MSG_HIST);
    msg_puts_attr(_("\nMaybe no changes were made or Vim did not update the swap file."),
                  attr | MSG_HIST);
    msg_end();
    goto theend;
  }
  b0p = hp->bh_data;
  if (STRNCMP(b0p->b0_version, "VIM 3.0", 7) == 0) {
    msg_start();
    msg_outtrans_attr(mfp->mf_fname, MSG_HIST);
    msg_puts_attr(_(" cannot be used with this version of Vim.\n"),
                  MSG_HIST);
    msg_puts_attr(_("Use Vim version 3.0.\n"), MSG_HIST);
    msg_end();
    goto theend;
  }
  if (ml_check_b0_id(b0p) == FAIL) {
    semsg(_("E307: %s does not look like a Vim swap file"), mfp->mf_fname);
    goto theend;
  }
  if (b0_magic_wrong(b0p)) {
    msg_start();
    msg_outtrans_attr(mfp->mf_fname, attr | MSG_HIST);
    msg_puts_attr(_(" cannot be used on this computer.\n"),
                  attr | MSG_HIST);
    msg_puts_attr(_("The file was created on "), attr | MSG_HIST);
    // avoid going past the end of a corrupted hostname
    b0p->b0_fname[0] = NUL;
    msg_puts_attr((char *)b0p->b0_hname, attr | MSG_HIST);
    msg_puts_attr(_(",\nor the file has been damaged."), attr | MSG_HIST);
    msg_end();
    goto theend;
  }

  /*
   * If we guessed the wrong page size, we have to recalculate the
   * highest block number in the file.
   */
  if (mfp->mf_page_size != (unsigned)char_to_long(b0p->b0_page_size)) {
    unsigned previous_page_size = mfp->mf_page_size;

    mf_new_page_size(mfp, (unsigned)char_to_long(b0p->b0_page_size));
    if (mfp->mf_page_size < previous_page_size) {
      msg_start();
      msg_outtrans_attr(mfp->mf_fname, attr | MSG_HIST);
      msg_puts_attr(_(" has been damaged (page size is smaller than minimum value).\n"),
                    attr | MSG_HIST);
      msg_end();
      goto theend;
    }
    if ((size = vim_lseek(mfp->mf_fd, (off_T)0L, SEEK_END)) <= 0) {
      mfp->mf_blocknr_max = 0;              // no file or empty file
    } else {
      mfp->mf_blocknr_max = size / mfp->mf_page_size;
    }
    mfp->mf_infile_count = mfp->mf_blocknr_max;

    // need to reallocate the memory used to store the data
    p = xmalloc(mfp->mf_page_size);
    memmove(p, hp->bh_data, previous_page_size);
    xfree(hp->bh_data);
    hp->bh_data = p;
    b0p = hp->bh_data;
  }

  /*
   * If .swp file name given directly, use name from swap file for buffer.
   */
  if (directly) {
    expand_env(b0p->b0_fname, NameBuff, MAXPATHL);
    if (setfname(curbuf, NameBuff, NULL, true) == FAIL) {
      goto theend;
    }
  }

  home_replace(NULL, mfp->mf_fname, NameBuff, MAXPATHL, TRUE);
  smsg(_("Using swap file \"%s\""), NameBuff);

  if (buf_spname(curbuf) != NULL) {
    STRLCPY(NameBuff, buf_spname(curbuf), MAXPATHL);
  } else {
    home_replace(NULL, curbuf->b_ffname, NameBuff, MAXPATHL, TRUE);
  }
  smsg(_("Original file \"%s\""), NameBuff);
  msg_putchar('\n');

  /*
   * check date of swap file and original file
   */
  FileInfo org_file_info;
  FileInfo swp_file_info;
  mtime = char_to_long(b0p->b0_mtime);
  if (curbuf->b_ffname != NULL
      && os_fileinfo((char *)curbuf->b_ffname, &org_file_info)
      && ((os_fileinfo((char *)mfp->mf_fname, &swp_file_info)
           && org_file_info.stat.st_mtim.tv_sec
           > swp_file_info.stat.st_mtim.tv_sec)
          || org_file_info.stat.st_mtim.tv_sec != mtime)) {
    emsg(_("E308: Warning: Original file may have been changed"));
  }
  ui_flush();

  // Get the 'fileformat' and 'fileencoding' from block zero.
  b0_ff = (b0p->b0_flags & B0_FF_MASK);
  if (b0p->b0_flags & B0_HAS_FENC) {
    int fnsize = B0_FNAME_SIZE_NOCRYPT;

    for (p = b0p->b0_fname + fnsize; p > b0p->b0_fname && p[-1] != NUL; p--) {
    }
    b0_fenc = vim_strnsave(p, b0p->b0_fname + fnsize - p);
  }

  mf_put(mfp, hp, false, false);        // release block 0
  hp = NULL;

  /*
   * Now that we are sure that the file is going to be recovered, clear the
   * contents of the current buffer.
   */
  while (!(curbuf->b_ml.ml_flags & ML_EMPTY)) {
    ml_delete((linenr_T)1, false);
  }

  /*
   * Try reading the original file to obtain the values of 'fileformat',
   * 'fileencoding', etc.  Ignore errors.  The text itself is not used.
   */
  if (curbuf->b_ffname != NULL) {
    orig_file_status = readfile(curbuf->b_ffname, NULL, (linenr_T)0,
                                (linenr_T)0, (linenr_T)MAXLNUM, NULL, READ_NEW);
  }

  // Use the 'fileformat' and 'fileencoding' as stored in the swap file.
  if (b0_ff != 0) {
    set_fileformat(b0_ff - 1, OPT_LOCAL);
  }
  if (b0_fenc != NULL) {
    set_option_value("fenc", 0L, (char *)b0_fenc, OPT_LOCAL);
    xfree(b0_fenc);
  }
  unchanged(curbuf, true, true);

  bnum = 1;             // start with block 1
  page_count = 1;       // which is 1 page
  lnum = 0;             // append after line 0 in curbuf
  line_count = 0;
  idx = 0;              // start with first index in block 1
  error = 0;
  buf->b_ml.ml_stack_top = 0;
  buf->b_ml.ml_stack = NULL;
  buf->b_ml.ml_stack_size = 0;          // no stack yet

  if (curbuf->b_ffname == NULL) {
    cannot_open = true;
  } else {
    cannot_open = false;
  }

  serious_error = false;
  for (; !got_int; line_breakcheck()) {
    if (hp != NULL) {
      mf_put(mfp, hp, false, false);            // release previous block
    }
    /*
     * get block
     */
    if ((hp = mf_get(mfp, bnum, page_count)) == NULL) {
      if (bnum == 1) {
        semsg(_("E309: Unable to read block 1 from %s"), mfp->mf_fname);
        goto theend;
      }
      ++error;
      ml_append(lnum++, (char_u *)_("???MANY LINES MISSING"),
                (colnr_T)0, true);
    } else {          // there is a block
      pp = hp->bh_data;
      if (pp->pb_id == PTR_ID) {                // it is a pointer block
        // check line count when using pointer block first time
        if (idx == 0 && line_count != 0) {
          for (i = 0; i < (int)pp->pb_count; ++i) {
            line_count -= pp->pb_pointer[i].pe_line_count;
          }
          if (line_count != 0) {
            ++error;
            ml_append(lnum++, (char_u *)_("???LINE COUNT WRONG"),
                      (colnr_T)0, true);
          }
        }

        if (pp->pb_count == 0) {
          ml_append(lnum++, (char_u *)_("???EMPTY BLOCK"),
                    (colnr_T)0, true);
          error++;
        } else if (idx < (int)pp->pb_count) {         // go a block deeper
          if (pp->pb_pointer[idx].pe_bnum < 0) {
            /*
             * Data block with negative block number.
             * Try to read lines from the original file.
             * This is slow, but it works.
             */
            if (!cannot_open) {
              line_count = pp->pb_pointer[idx].pe_line_count;
              if (readfile(curbuf->b_ffname, NULL, lnum,
                           pp->pb_pointer[idx].pe_old_lnum - 1, line_count,
                           NULL, 0) != OK) {
                cannot_open = true;
              } else {
                lnum += line_count;
              }
            }
            if (cannot_open) {
              ++error;
              ml_append(lnum++, (char_u *)_("???LINES MISSING"),
                        (colnr_T)0, true);
            }
            ++idx;                  // get same block again for next index
            continue;
          }

          /*
           * going one block deeper in the tree
           */
          top = ml_add_stack(buf);  // new entry in stack
          ip = &(buf->b_ml.ml_stack[top]);
          ip->ip_bnum = bnum;
          ip->ip_index = idx;

          bnum = pp->pb_pointer[idx].pe_bnum;
          line_count = pp->pb_pointer[idx].pe_line_count;
          page_count = pp->pb_pointer[idx].pe_page_count;
          idx = 0;
          continue;
        }
      } else {            // not a pointer block
        dp = hp->bh_data;
        if (dp->db_id != DATA_ID) {             // block id wrong
          if (bnum == 1) {
            semsg(_("E310: Block 1 ID wrong (%s not a .swp file?)"),
                  mfp->mf_fname);
            goto theend;
          }
          ++error;
          ml_append(lnum++, (char_u *)_("???BLOCK MISSING"),
                    (colnr_T)0, true);
        } else {
          // it is a data block
          // Append all the lines in this block
          has_error = false;
          // check length of block
          // if wrong, use length in pointer block
          if (page_count * mfp->mf_page_size != dp->db_txt_end) {
            ml_append(lnum++,
                      (char_u *)_("??? from here until ???END lines"
                                  " may be messed up"),
                      (colnr_T)0, true);
            error++;
            has_error = true;
            dp->db_txt_end = page_count * mfp->mf_page_size;
          }

          // make sure there is a NUL at the end of the block
          *((char_u *)dp + dp->db_txt_end - 1) = NUL;

          /*
           * check number of lines in block
           * if wrong, use count in data block
           */
          if (line_count != dp->db_line_count) {
            ml_append(lnum++,
                      (char_u *)_("??? from here until ???END lines"
                                  " may have been inserted/deleted"),
                      (colnr_T)0, true);
            error++;
            has_error = true;
          }

          for (i = 0; i < dp->db_line_count; ++i) {
            txt_start = (dp->db_index[i] & DB_INDEX_MASK);
            if (txt_start <= (int)HEADER_SIZE
                || txt_start >= (int)dp->db_txt_end) {
              p = (char_u *)"???";
              ++error;
            } else {
              p = (char_u *)dp + txt_start;
            }
            ml_append(lnum++, p, (colnr_T)0, true);
          }
          if (has_error) {
            ml_append(lnum++, (char_u *)_("???END"), (colnr_T)0, true);
          }
        }
      }
    }

    if (buf->b_ml.ml_stack_top == 0) {          // finished
      break;
    }

    /*
     * go one block up in the tree
     */
    ip = &(buf->b_ml.ml_stack[--(buf->b_ml.ml_stack_top)]);
    bnum = ip->ip_bnum;
    idx = ip->ip_index + 1;         // go to next index
    page_count = 1;
  }

  /*
   * Compare the buffer contents with the original file.  When they differ
   * set the 'modified' flag.
   * Lines 1 - lnum are the new contents.
   * Lines lnum + 1 to ml_line_count are the original contents.
   * Line ml_line_count + 1 in the dummy empty line.
   */
  if (orig_file_status != OK || curbuf->b_ml.ml_line_count != lnum * 2 + 1) {
    // Recovering an empty file results in two lines and the first line is
    // empty.  Don't set the modified flag then.
    if (!(curbuf->b_ml.ml_line_count == 2 && *ml_get(1) == NUL)) {
      changed_internal();
      buf_inc_changedtick(curbuf);
    }
  } else {
    for (idx = 1; idx <= lnum; ++idx) {
      // Need to copy one line, fetching the other one may flush it.
      p = vim_strsave(ml_get(idx));
      i = STRCMP(p, ml_get(idx + lnum));
      xfree(p);
      if (i != 0) {
        changed_internal();
        buf_inc_changedtick(curbuf);
        break;
      }
    }
  }

  /*
   * Delete the lines from the original file and the dummy line from the
   * empty buffer.  These will now be after the last line in the buffer.
   */
  while (curbuf->b_ml.ml_line_count > lnum
         && !(curbuf->b_ml.ml_flags & ML_EMPTY)) {
    ml_delete(curbuf->b_ml.ml_line_count, false);
  }
  curbuf->b_flags |= BF_RECOVERED;
  check_cursor();

  recoverymode = FALSE;
  if (got_int) {
    emsg(_("E311: Recovery Interrupted"));
  } else if (error) {
    ++no_wait_return;
    msg(">>>>>>>>>>>>>");
    emsg(_("E312: Errors detected while recovering; look for lines starting with ???"));
    --no_wait_return;
    msg(_("See \":help E312\" for more information."));
    msg(">>>>>>>>>>>>>");
  } else {
    if (curbuf->b_changed) {
      msg(_("Recovery completed. You should check if everything is OK."));
      msg_puts(_("\n(You might want to write out this file under another name\n"));
      msg_puts(_("and run diff with the original file to check for changes)"));
    } else {
      msg(_("Recovery completed. Buffer contents equals file contents."));
    }
    msg_puts(_("\nYou may want to delete the .swp file now.\n\n"));
    cmdline_row = msg_row;
  }
  redraw_curbuf_later(NOT_VALID);

theend:
  xfree(fname_used);
  recoverymode = FALSE;
  if (mfp != NULL) {
    if (hp != NULL) {
      mf_put(mfp, hp, false, false);
    }
    mf_close(mfp, false);           // will also xfree(mfp->mf_fname)
  }
  if (buf != NULL) {  //may be NULL if swap file not found.
    xfree(buf->b_ml.ml_stack);
    xfree(buf);
  }
  if (serious_error && called_from_main) {
    ml_close(curbuf, TRUE);
  } else {
    apply_autocmds(EVENT_BUFREADPOST, NULL, curbuf->b_fname, FALSE, curbuf);
    apply_autocmds(EVENT_BUFWINENTER, NULL, curbuf->b_fname, FALSE, curbuf);
  }
}

/// Find the names of swap files in current directory and the directory given
/// with the 'directory' option.
///
/// Used to:
/// - list the swap files for "vim -r"
/// - count the number of swap files when recovering
/// - list the swap files when recovering
/// - find the name of the n'th swap file when recovering
///
/// @param fname  base for swap file name
/// @param list  when TRUE, list the swap file names
/// @param nr  when non-zero, return nr'th swap file name
/// @param fname_out  result when "nr" > 0
int recover_names(char_u *fname, int list, int nr, char_u **fname_out)
{
  int num_names;
  char_u *(names[6]);
  char_u *tail;
  char_u *p;
  int num_files;
  int file_count = 0;
  char_u **files;
  char_u *dirp;
  char_u *dir_name;
  char_u *fname_res = NULL;
#ifdef HAVE_READLINK
  char_u fname_buf[MAXPATHL];
#endif

  if (fname != NULL) {
#ifdef HAVE_READLINK
    // Expand symlink in the file name, because the swap file is created
    // with the actual file instead of with the symlink.
    if (resolve_symlink(fname, fname_buf) == OK) {
      fname_res = fname_buf;
    } else
#endif
    fname_res = fname;
  }

  if (list) {
    // use msg() to start the scrolling properly
    msg(_("Swap files found:"));
    msg_putchar('\n');
  }

  // Do the loop for every directory in 'directory'.
  // First allocate some memory to put the directory name in.
  dir_name = xmalloc(STRLEN(p_dir) + 1);
  dirp = p_dir;
  while (*dirp) {
    // Isolate a directory name from *dirp and put it in dir_name (we know
    // it is large enough, so use 31000 for length).
    // Advance dirp to next directory name.
    (void)copy_option_part(&dirp, dir_name, 31000, ",");

    if (dir_name[0] == '.' && dir_name[1] == NUL) {     // check current dir
      if (fname == NULL) {
        names[0] = vim_strsave((char_u *)"*.sw?");
        // For Unix names starting with a dot are special.  MS-Windows
        // supports this too, on some file systems.
        names[1] = vim_strsave((char_u *)".*.sw?");
        names[2] = vim_strsave((char_u *)".sw?");
        num_names = 3;
      } else {
        num_names = recov_file_names(names, fname_res, TRUE);
      }
    } else {                      // check directory dir_name
      if (fname == NULL) {
        names[0] = (char_u *)concat_fnames((char *)dir_name, "*.sw?", true);
        // For Unix names starting with a dot are special.  MS-Windows
        // supports this too, on some file systems.
        names[1] = (char_u *)concat_fnames((char *)dir_name, ".*.sw?", true);
        names[2] = (char_u *)concat_fnames((char *)dir_name, ".sw?", true);
        num_names = 3;
      } else {
        int len = (int)STRLEN(dir_name);
        p = dir_name + len;
        if (after_pathsep((char *)dir_name, (char *)p)
            && len > 1
            && p[-1] == p[-2]) {
          // Ends with '//', Use Full path for swap name
          tail = (char_u *)make_percent_swname((char *)dir_name,
                                               (char *)fname_res);
        } else {
          tail = path_tail(fname_res);
          tail = (char_u *)concat_fnames((char *)dir_name, (char *)tail, TRUE);
        }
        num_names = recov_file_names(names, tail, FALSE);
        xfree(tail);
      }
    }

    if (num_names == 0) {
      num_files = 0;
    } else if (expand_wildcards(num_names, names, &num_files, &files,
                                EW_KEEPALL|EW_FILE|EW_SILENT) == FAIL) {
      num_files = 0;
    }

    /*
     * When no swap file found, wildcard expansion might have failed (e.g.
     * not able to execute the shell).
     * Try finding a swap file by simply adding ".swp" to the file name.
     */
    if (*dirp == NUL && file_count + num_files == 0 && fname != NULL) {
      char_u *swapname = (char_u *)modname((char *)fname_res, ".swp", true);
      if (swapname != NULL) {
        if (os_path_exists(swapname)) {
          files = xmalloc(sizeof(char_u *));
          files[0] = swapname;
          swapname = NULL;
          num_files = 1;
        }
        xfree(swapname);
      }
    }

    /*
     * remove swapfile name of the current buffer, it must be ignored
     */
    if (curbuf->b_ml.ml_mfp != NULL
        && (p = curbuf->b_ml.ml_mfp->mf_fname) != NULL) {
      for (int i = 0; i < num_files; i++) {
        // Do not expand wildcards, on Windows would try to expand
        // "%tmp%" in "%tmp%file"
        if (path_full_compare(p, files[i], true, false) & kEqualFiles) {
          // Remove the name from files[i].  Move further entries
          // down.  When the array becomes empty free it here, since
          // FreeWild() won't be called below.
          xfree(files[i]);
          if (--num_files == 0) {
            xfree(files);
          } else {
            for (; i < num_files; ++i) {
              files[i] = files[i + 1];
            }
          }
        }
      }
    }
    if (nr > 0) {
      file_count += num_files;
      if (nr <= file_count) {
        *fname_out = vim_strsave(files[nr - 1 + num_files - file_count]);
        dirp = (char_u *)"";                        // stop searching
      }
    } else if (list) {
      if (dir_name[0] == '.' && dir_name[1] == NUL) {
        if (fname == NULL) {
          msg_puts(_("   In current directory:\n"));
        } else {
          msg_puts(_("   Using specified name:\n"));
        }
      } else {
        msg_puts(_("   In directory "));
        msg_home_replace(dir_name);
        msg_puts(":\n");
      }

      if (num_files) {
        for (int i = 0; i < num_files; ++i) {
          // print the swap file name
          msg_outnum((long)++file_count);
          msg_puts(".    ");
          msg_puts((const char *)path_tail(files[i]));
          msg_putchar('\n');
          (void)swapfile_info(files[i]);
        }
      } else {
        msg_puts(_("      -- none --\n"));
      }
      ui_flush();
    } else {
      file_count += num_files;
    }

    for (int i = 0; i < num_names; ++i) {
      xfree(names[i]);
    }
    if (num_files > 0) {
      FreeWild(num_files, files);
    }
  }
  xfree(dir_name);
  return file_count;
}

/*
 * Append the full path to name with path separators made into percent
 * signs, to dir. An unnamed buffer is handled as "" (<currentdir>/"")
 */
char *make_percent_swname(const char *dir, const char *name)
  FUNC_ATTR_NONNULL_ARG(1)
{
  char *d = NULL;
  char *f = fix_fname(name != NULL ? name : "");
  if (f != NULL) {
    char *s = xstrdup(f);
    for (d = s; *d != NUL; MB_PTR_ADV(d)) {
      if (vim_ispathsep(*d)) {
        *d = '%';
      }
    }
    d = concat_fnames(dir, s, TRUE);
    xfree(s);
    xfree(f);
  }
  return d;
}

static bool process_still_running;

/// Return information found in swapfile "fname" in dictionary "d".
/// This is used by the swapinfo() function.
void get_b0_dict(const char *fname, dict_T *d)
{
  int fd;
  struct block0 b0;

  if ((fd = os_open(fname, O_RDONLY, 0)) >= 0) {
    if (read_eintr(fd, &b0, sizeof(b0)) == sizeof(b0)) {
      if (ml_check_b0_id(&b0) == FAIL) {
        tv_dict_add_str(d, S_LEN("error"), "Not a swap file");
      } else if (b0_magic_wrong(&b0)) {
        tv_dict_add_str(d, S_LEN("error"), "Magic number mismatch");
      } else {
        // We have swap information.
        tv_dict_add_str_len(d, S_LEN("version"), (char *)b0.b0_version, 10);
        tv_dict_add_str_len(d, S_LEN("user"), (char *)b0.b0_uname,
                            B0_UNAME_SIZE);
        tv_dict_add_str_len(d, S_LEN("host"), (char *)b0.b0_hname,
                            B0_HNAME_SIZE);
        tv_dict_add_str_len(d, S_LEN("fname"), (char *)b0.b0_fname,
                            B0_FNAME_SIZE_ORG);

        tv_dict_add_nr(d, S_LEN("pid"), char_to_long(b0.b0_pid));
        tv_dict_add_nr(d, S_LEN("mtime"), char_to_long(b0.b0_mtime));
        tv_dict_add_nr(d, S_LEN("dirty"), b0.b0_dirty ? 1 : 0);
        tv_dict_add_nr(d, S_LEN("inode"), char_to_long(b0.b0_ino));
      }
    } else {
      tv_dict_add_str(d, S_LEN("error"), "Cannot read file");
    }
    close(fd);
  } else {
    tv_dict_add_str(d, S_LEN("error"), "Cannot open file");
  }
}

/// Give information about an existing swap file.
/// Returns timestamp (0 when unknown).
static time_t swapfile_info(char_u *fname)
{
  assert(fname != NULL);
  int fd;
  struct block0 b0;
  time_t x = (time_t)0;
#ifdef UNIX
  char uname[B0_UNAME_SIZE];
#endif

  // print the swap file date
  FileInfo file_info;
  if (os_fileinfo((char *)fname, &file_info)) {
#ifdef UNIX
    // print name of owner of the file
    if (os_get_uname(file_info.stat.st_uid, uname, B0_UNAME_SIZE) == OK) {
      msg_puts(_("          owned by: "));
      msg_outtrans((char_u *)uname);
      msg_puts(_("   dated: "));
    } else
#endif
    msg_puts(_("             dated: "));
    x = file_info.stat.st_mtim.tv_sec;
    char ctime_buf[50];
    msg_puts(os_ctime_r(&x, ctime_buf, sizeof(ctime_buf)));
  }

  /*
   * print the original file name
   */
  fd = os_open((char *)fname, O_RDONLY, 0);
  if (fd >= 0) {
    if (read_eintr(fd, &b0, sizeof(b0)) == sizeof(b0)) {
      if (STRNCMP(b0.b0_version, "VIM 3.0", 7) == 0) {
        msg_puts(_("         [from Vim version 3.0]"));
      } else if (ml_check_b0_id(&b0) == FAIL) {
        msg_puts(_("         [does not look like a Vim swap file]"));
      } else if (!ml_check_b0_strings(&b0)) {
        msg_puts(_("         [garbled strings (not nul terminated)]"));
      } else {
        msg_puts(_("         file name: "));
        if (b0.b0_fname[0] == NUL) {
          msg_puts(_("[No Name]"));
        } else {
          msg_outtrans(b0.b0_fname);
        }

        msg_puts(_("\n          modified: "));
        msg_puts(b0.b0_dirty ? _("YES") : _("no"));

        if (*(b0.b0_uname) != NUL) {
          msg_puts(_("\n         user name: "));
          msg_outtrans(b0.b0_uname);
        }

        if (*(b0.b0_hname) != NUL) {
          if (*(b0.b0_uname) != NUL) {
            msg_puts(_("   host name: "));
          } else {
            msg_puts(_("\n         host name: "));
          }
          msg_outtrans(b0.b0_hname);
        }

        if (char_to_long(b0.b0_pid) != 0L) {
          msg_puts(_("\n        process ID: "));
          msg_outnum(char_to_long(b0.b0_pid));
          if (os_proc_running((int)char_to_long(b0.b0_pid))) {
            msg_puts(_(" (STILL RUNNING)"));
            process_still_running = true;
          }
        }

        if (b0_magic_wrong(&b0)) {
          msg_puts(_("\n         [not usable on this computer]"));
        }
      }
    } else {
      msg_puts(_("         [cannot be read]"));
    }
    close(fd);
  } else {
    msg_puts(_("         [cannot be opened]"));
  }
  msg_putchar('\n');

  return x;
}

/// Returns TRUE if the swap file looks OK and there are no changes, thus it
/// can be safely deleted.
static time_t swapfile_unchanged(char *fname)
{
  struct block0 b0;
  int ret = true;

  // Swap file must exist.
  if (!os_path_exists((char_u *)fname)) {
    return false;
  }

  // must be able to read the first block
  int fd = os_open(fname, O_RDONLY, 0);
  if (fd < 0) {
    return false;
  }
  if (read_eintr(fd, &b0, sizeof(b0)) != sizeof(b0)) {
    close(fd);
    return false;
  }

  // the ID and magic number must be correct
  if (ml_check_b0_id(&b0) == FAIL || b0_magic_wrong(&b0)) {
    ret = false;
  }

  // must be unchanged
  if (b0.b0_dirty) {
    ret = false;
  }

  // process must be known and not running.
  long pid = char_to_long(b0.b0_pid);
  if (pid == 0L || os_proc_running((int)pid)) {
    ret = false;
  }

  // TODO(bram): Should we check if the swap file was created on the current
  // system?  And the current user?

  close(fd);
  return ret;
}

static int recov_file_names(char_u **names, char_u *path, int prepend_dot)
  FUNC_ATTR_NONNULL_ALL
{
  int num_names = 0;

  // May also add the file name with a dot prepended, for swap file in same
  // dir as original file.
  if (prepend_dot) {
    names[num_names] = (char_u *)modname((char *)path, ".sw?", true);
    if (names[num_names] == NULL) {
      return num_names;
    }
    num_names++;
  }

  // Form the normal swap file name pattern by appending ".sw?".
  names[num_names] = (char_u *)concat_fnames((char *)path, ".sw?", FALSE);
  if (num_names >= 1) {     // check if we have the same name twice
    char_u *p = names[num_names - 1];
    int i = (int)STRLEN(names[num_names - 1]) - (int)STRLEN(names[num_names]);
    if (i > 0) {
      p += i;               // file name has been expanded to full path
    }
    if (STRCMP(p, names[num_names]) != 0) {
      ++num_names;
    } else {
      xfree(names[num_names]);
    }
  } else {
    ++num_names;
  }

  return num_names;
}

/*
 * sync all memlines
 *
 * If 'check_file' is TRUE, check if original file exists and was not changed.
 * If 'check_char' is TRUE, stop syncing when character becomes available, but
 * always sync at least one block.
 */
void ml_sync_all(int check_file, int check_char, bool do_fsync)
{
  FOR_ALL_BUFFERS(buf) {
    if (buf->b_ml.ml_mfp == NULL || buf->b_ml.ml_mfp->mf_fname == NULL) {
      continue;                             // no file
    }
    ml_flush_line(buf);                     // flush buffered line
                                            // flush locked block
    (void)ml_find_line(buf, (linenr_T)0, ML_FLUSH);
    if (bufIsChanged(buf) && check_file && mf_need_trans(buf->b_ml.ml_mfp)
        && buf->b_ffname != NULL) {
      /*
       * If the original file does not exist anymore or has been changed
       * call ml_preserve() to get rid of all negative numbered blocks.
       */
      FileInfo file_info;
      if (!os_fileinfo((char *)buf->b_ffname, &file_info)
          || file_info.stat.st_mtim.tv_sec != buf->b_mtime_read
          || os_fileinfo_size(&file_info) != buf->b_orig_size) {
        ml_preserve(buf, false, do_fsync);
        did_check_timestamps = false;
        need_check_timestamps = true;           // give message later
      }
    }
    if (buf->b_ml.ml_mfp->mf_dirty) {
      (void)mf_sync(buf->b_ml.ml_mfp, (check_char ? MFS_STOP : 0)
                    | (do_fsync && bufIsChanged(buf) ? MFS_FLUSH : 0));
      if (check_char && os_char_avail()) {      // character available now
        break;
      }
    }
  }
}

/*
 * sync one buffer, including negative blocks
 *
 * after this all the blocks are in the swap file
 *
 * Used for the :preserve command and when the original file has been
 * changed or deleted.
 *
 * when message is TRUE the success of preserving is reported
 */
void ml_preserve(buf_T *buf, int message, bool do_fsync)
{
  bhdr_T *hp;
  linenr_T lnum;
  memfile_T *mfp = buf->b_ml.ml_mfp;
  int status;
  int got_int_save = got_int;

  if (mfp == NULL || mfp->mf_fname == NULL) {
    if (message) {
      emsg(_("E313: Cannot preserve, there is no swap file"));
    }
    return;
  }

  // We only want to stop when interrupted here, not when interrupted
  // before.
  got_int = false;

  ml_flush_line(buf);                               // flush buffered line
  (void)ml_find_line(buf, (linenr_T)0, ML_FLUSH);   // flush locked block
  status = mf_sync(mfp, MFS_ALL | (do_fsync ? MFS_FLUSH : 0));

  // stack is invalid after mf_sync(.., MFS_ALL)
  buf->b_ml.ml_stack_top = 0;

  /*
   * Some of the data blocks may have been changed from negative to
   * positive block number. In that case the pointer blocks need to be
   * updated.
   *
   * We don't know in which pointer block the references are, so we visit
   * all data blocks until there are no more translations to be done (or
   * we hit the end of the file, which can only happen in case a write fails,
   * e.g. when file system if full).
   * ml_find_line() does the work by translating the negative block numbers
   * when getting the first line of each data block.
   */
  if (mf_need_trans(mfp) && !got_int) {
    lnum = 1;
    while (mf_need_trans(mfp) && lnum <= buf->b_ml.ml_line_count) {
      hp = ml_find_line(buf, lnum, ML_FIND);
      if (hp == NULL) {
        status = FAIL;
        goto theend;
      }
      CHECK(buf->b_ml.ml_locked_low != lnum, "low != lnum");
      lnum = buf->b_ml.ml_locked_high + 1;
    }
    (void)ml_find_line(buf, (linenr_T)0, ML_FLUSH);  // flush locked block
    // sync the updated pointer blocks
    if (mf_sync(mfp, MFS_ALL | (do_fsync ? MFS_FLUSH : 0)) == FAIL) {
      status = FAIL;
    }
    buf->b_ml.ml_stack_top = 0;  // stack is invalid now
  }
theend:
  got_int |= got_int_save;

  if (message) {
    if (status == OK) {
      msg(_("File preserved"));
    } else {
      emsg(_("E314: Preserve failed"));
    }
  }
}

/*
 * NOTE: The pointer returned by the ml_get_*() functions only remains valid
 * until the next call!
 *  line1 = ml_get(1);
 *  line2 = ml_get(2);  // line1 is now invalid!
 * Make a copy of the line if necessary.
 */
/*
 * Return a pointer to a (read-only copy of a) line.
 *
 * On failure an error message is given and IObuff is returned (to avoid
 * having to check for error everywhere).
 */
char_u *ml_get(linenr_T lnum)
{
  return ml_get_buf(curbuf, lnum, false);
}

/*
 * Return pointer to position "pos".
 */
char_u *ml_get_pos(const pos_T *pos)
  FUNC_ATTR_NONNULL_ALL
{
  return ml_get_buf(curbuf, pos->lnum, false) + pos->col;
}

/// Return a pointer to a line in a specific buffer
///
/// @param will_change  true mark the buffer dirty (chars in the line will be changed)
char_u *ml_get_buf(buf_T *buf, linenr_T lnum, bool will_change)
  FUNC_ATTR_NONNULL_ALL
{
  bhdr_T *hp;
  DATA_BL *dp;
  char_u *ptr;
  static int recursive = 0;

  if (lnum > buf->b_ml.ml_line_count) {  // invalid line number
    if (recursive == 0) {
      // Avoid giving this message for a recursive call, may happen when
      // the GUI redraws part of the text.
      recursive++;
      siemsg(_("E315: ml_get: invalid lnum: %" PRId64), (int64_t)lnum);
      recursive--;
    }
errorret:
    STRCPY(IObuff, "???");
    return IObuff;
  }
  if (lnum <= 0) {                      // pretend line 0 is line 1
    lnum = 1;
  }

  if (buf->b_ml.ml_mfp == NULL) {       // there are no lines
    return (char_u *)"";
  }

  /*
   * See if it is the same line as requested last time.
   * Otherwise may need to flush last used line.
   * Don't use the last used line when 'swapfile' is reset, need to load all
   * blocks.
   */
  if (buf->b_ml.ml_line_lnum != lnum) {
    ml_flush_line(buf);

    /*
     * Find the data block containing the line.
     * This also fills the stack with the blocks from the root to the data
     * block and releases any locked block.
     */
    if ((hp = ml_find_line(buf, lnum, ML_FIND)) == NULL) {
      if (recursive == 0) {
        // Avoid giving this message for a recursive call, may happen
        // when the GUI redraws part of the text.
        recursive++;
        get_trans_bufname(buf);
        shorten_dir(NameBuff);
        siemsg(_("E316: ml_get: cannot find line %" PRId64 " in buffer %d %s"),
               (int64_t)lnum, buf->b_fnum, NameBuff);
        recursive--;
      }
      goto errorret;
    }

    dp = hp->bh_data;

    ptr = (char_u *)dp +
          ((dp->db_index[lnum - buf->b_ml.ml_locked_low]) & DB_INDEX_MASK);
    buf->b_ml.ml_line_ptr = ptr;
    buf->b_ml.ml_line_lnum = lnum;
    buf->b_ml.ml_flags &= ~ML_LINE_DIRTY;
  }
  if (will_change) {
    buf->b_ml.ml_flags |= (ML_LOCKED_DIRTY | ML_LOCKED_POS);
    ml_add_deleted_len_buf(buf, buf->b_ml.ml_line_ptr, -1);
  }

  return buf->b_ml.ml_line_ptr;
}

/*
 * Check if a line that was just obtained by a call to ml_get
 * is in allocated memory.
 */
int ml_line_alloced(void)
{
  return curbuf->b_ml.ml_flags & ML_LINE_DIRTY;
}

/// Append a line after lnum (may be 0 to insert a line in front of the file).
/// "line" does not need to be allocated, but can't be another line in a
/// buffer, unlocking may make it invalid.
///
///   newfile: TRUE when starting to edit a new file, meaning that pe_old_lnum
///              will be set for recovery
/// Check: The caller of this function should probably also call
/// appended_lines().
///
/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of new line, including NUL, or 0
/// @param newfile  flag, see above
///
/// @return  FAIL for failure, OK otherwise
int ml_append(linenr_T lnum, char_u *line, colnr_T len, bool newfile)
{
  // When starting up, we might still need to create the memfile
  if (curbuf->b_ml.ml_mfp == NULL && open_buffer(FALSE, NULL, 0) == FAIL) {
    return FAIL;
  }

  if (curbuf->b_ml.ml_line_lnum != 0) {
    ml_flush_line(curbuf);
  }
  return ml_append_int(curbuf, lnum, line, len, newfile, FALSE);
}

/// Like ml_append() but for an arbitrary buffer.  The buffer must already have
/// a memline.
///
/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of new line, including NUL, or 0
/// @param newfile  flag, see above
int ml_append_buf(buf_T *buf, linenr_T lnum, char_u *line, colnr_T len, bool newfile)
  FUNC_ATTR_NONNULL_ARG(1)
{
  if (buf->b_ml.ml_mfp == NULL) {
    return FAIL;
  }

  if (buf->b_ml.ml_line_lnum != 0) {
    ml_flush_line(buf);
  }
  return ml_append_int(buf, lnum, line, len, newfile, FALSE);
}

/// @param lnum  append after this line (can be 0)
/// @param line  text of the new line
/// @param len  length of line, including NUL, or 0
/// @param newfile  flag, see above
/// @param mark  mark the new line
static int ml_append_int(buf_T *buf, linenr_T lnum, char_u *line, colnr_T len, bool newfile,
                         int mark)
{
  int i;
  int line_count;               // number of indexes in current block
  int offset;
  int from, to;
  int space_needed;             // space needed for new line
  int page_size;
  int page_count;
  int db_idx;                   // index for lnum in data block
  bhdr_T *hp;
  memfile_T *mfp;
  DATA_BL *dp;
  PTR_BL *pp;
  infoptr_T *ip;

  // lnum out of range
  if (lnum > buf->b_ml.ml_line_count || buf->b_ml.ml_mfp == NULL) {
    return FAIL;
  }

  if (lowest_marked && lowest_marked > lnum) {
    lowest_marked = lnum + 1;
  }

  if (len == 0) {
    len = (colnr_T)STRLEN(line) + 1;            // space needed for the text
  }
  space_needed = len + INDEX_SIZE;      // space needed for text + index

  mfp = buf->b_ml.ml_mfp;
  page_size = mfp->mf_page_size;

  /*
   * find the data block containing the previous line
   * This also fills the stack with the blocks from the root to the data block
   * This also releases any locked block.
   */
  if ((hp = ml_find_line(buf, lnum == 0 ? (linenr_T)1 : lnum,
                         ML_INSERT)) == NULL) {
    return FAIL;
  }

  buf->b_ml.ml_flags &= ~ML_EMPTY;

  if (lnum == 0) {              // got line one instead, correct db_idx
    db_idx = -1;                // careful, it is negative!
  } else {
    db_idx = lnum - buf->b_ml.ml_locked_low;
  }
  // get line count before the insertion
  line_count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low;

  dp = hp->bh_data;

  /*
   * If
   * - there is not enough room in the current block
   * - appending to the last line in the block
   * - not appending to the last line in the file
   * insert in front of the next block.
   */
  if ((int)dp->db_free < space_needed && db_idx == line_count - 1
      && lnum < buf->b_ml.ml_line_count) {
    /*
     * Now that the line is not going to be inserted in the block that we
     * expected, the line count has to be adjusted in the pointer blocks
     * by using ml_locked_lineadd.
     */
    --(buf->b_ml.ml_locked_lineadd);
    --(buf->b_ml.ml_locked_high);
    if ((hp = ml_find_line(buf, lnum + 1, ML_INSERT)) == NULL) {
      return FAIL;
    }

    db_idx = -1;                    // careful, it is negative!
    // get line count before the insertion
    line_count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low;
    CHECK(buf->b_ml.ml_locked_low != lnum + 1, "locked_low != lnum + 1");

    dp = hp->bh_data;
  }

  ++buf->b_ml.ml_line_count;

  if ((int)dp->db_free >= space_needed) {       // enough room in data block
    /*
     * Insert new line in existing data block, or in data block allocated above.
     */
    dp->db_txt_start -= len;
    dp->db_free -= space_needed;
    ++(dp->db_line_count);

    /*
     * move the text of the lines that follow to the front
     * adjust the indexes of the lines that follow
     */
    if (line_count > db_idx + 1) {          // if there are following lines
      /*
       * Offset is the start of the previous line.
       * This will become the character just after the new line.
       */
      if (db_idx < 0) {
        offset = dp->db_txt_end;
      } else {
        offset = ((dp->db_index[db_idx]) & DB_INDEX_MASK);
      }
      memmove((char *)dp + dp->db_txt_start,
              (char *)dp + dp->db_txt_start + len,
              (size_t)(offset - (dp->db_txt_start + len)));
      for (i = line_count - 1; i > db_idx; --i) {
        dp->db_index[i + 1] = dp->db_index[i] - len;
      }
      dp->db_index[db_idx + 1] = offset - len;
    } else {  // add line at the end
      dp->db_index[db_idx + 1] = dp->db_txt_start;
    }

    /*
     * copy the text into the block
     */
    memmove((char *)dp + dp->db_index[db_idx + 1], line, (size_t)len);
    if (mark) {
      dp->db_index[db_idx + 1] |= DB_MARKED;
    }

    /*
     * Mark the block dirty.
     */
    buf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
    if (!newfile) {
      buf->b_ml.ml_flags |= ML_LOCKED_POS;
    }
  } else {        // not enough space in data block
    /*
     * If there is not enough room we have to create a new data block and copy some
     * lines into it.
     * Then we have to insert an entry in the pointer block.
     * If this pointer block also is full, we go up another block, and so on, up
     * to the root if necessary.
     * The line counts in the pointer blocks have already been adjusted by
     * ml_find_line().
     */
    long line_count_left, line_count_right;
    int page_count_left, page_count_right;
    bhdr_T *hp_left;
    bhdr_T *hp_right;
    bhdr_T *hp_new;
    int lines_moved;
    int data_moved = 0;                     // init to shut up gcc
    int total_moved = 0;                    // init to shut up gcc
    DATA_BL *dp_right, *dp_left;
    int stack_idx;
    bool in_left;
    int lineadd;
    blocknr_T bnum_left, bnum_right;
    linenr_T lnum_left, lnum_right;
    int pb_idx;
    PTR_BL *pp_new;

    /*
     * We are going to allocate a new data block. Depending on the
     * situation it will be put to the left or right of the existing
     * block.  If possible we put the new line in the left block and move
     * the lines after it to the right block. Otherwise the new line is
     * also put in the right block. This method is more efficient when
     * inserting a lot of lines at one place.
     */
    if (db_idx < 0) {           // left block is new, right block is existing
      lines_moved = 0;
      in_left = true;
      // space_needed does not change
    } else {                  // left block is existing, right block is new
      lines_moved = line_count - db_idx - 1;
      if (lines_moved == 0) {
        in_left = false;                // put new line in right block
                                        // space_needed does not change
      } else {
        data_moved = ((dp->db_index[db_idx]) & DB_INDEX_MASK) -
                     dp->db_txt_start;
        total_moved = data_moved + lines_moved * INDEX_SIZE;
        if ((int)dp->db_free + total_moved >= space_needed) {
          in_left = true;               // put new line in left block
          space_needed = total_moved;
        } else {
          in_left = false;                  // put new line in right block
          space_needed += total_moved;
        }
      }
    }

    page_count = ((space_needed + HEADER_SIZE) + page_size - 1) / page_size;
    hp_new = ml_new_data(mfp, newfile, page_count);
    if (db_idx < 0) {           // left block is new
      hp_left = hp_new;
      hp_right = hp;
      line_count_left = 0;
      line_count_right = line_count;
    } else {                  // right block is new
      hp_left = hp;
      hp_right = hp_new;
      line_count_left = line_count;
      line_count_right = 0;
    }
    dp_right = hp_right->bh_data;
    dp_left = hp_left->bh_data;
    bnum_left = hp_left->bh_bnum;
    bnum_right = hp_right->bh_bnum;
    page_count_left = hp_left->bh_page_count;
    page_count_right = hp_right->bh_page_count;

    /*
     * May move the new line into the right/new block.
     */
    if (!in_left) {
      dp_right->db_txt_start -= len;
      dp_right->db_free -= len + INDEX_SIZE;
      dp_right->db_index[0] = dp_right->db_txt_start;
      if (mark) {
        dp_right->db_index[0] |= DB_MARKED;
      }

      memmove((char *)dp_right + dp_right->db_txt_start,
              line, (size_t)len);
      ++line_count_right;
    }
    /*
     * may move lines from the left/old block to the right/new one.
     */
    if (lines_moved) {
      /*
       */
      dp_right->db_txt_start -= data_moved;
      dp_right->db_free -= total_moved;
      memmove((char *)dp_right + dp_right->db_txt_start,
              (char *)dp_left + dp_left->db_txt_start,
              (size_t)data_moved);
      offset = dp_right->db_txt_start - dp_left->db_txt_start;
      dp_left->db_txt_start += data_moved;
      dp_left->db_free += total_moved;

      /*
       * update indexes in the new block
       */
      for (to = line_count_right, from = db_idx + 1;
           from < line_count_left; ++from, ++to) {
        dp_right->db_index[to] = dp->db_index[from] + offset;
      }
      line_count_right += lines_moved;
      line_count_left -= lines_moved;
    }

    /*
     * May move the new line into the left (old or new) block.
     */
    if (in_left) {
      dp_left->db_txt_start -= len;
      dp_left->db_free -= len + INDEX_SIZE;
      dp_left->db_index[line_count_left] = dp_left->db_txt_start;
      if (mark) {
        dp_left->db_index[line_count_left] |= DB_MARKED;
      }
      memmove((char *)dp_left + dp_left->db_txt_start,
              line, (size_t)len);
      ++line_count_left;
    }

    if (db_idx < 0) {           // left block is new
      lnum_left = lnum + 1;
      lnum_right = 0;
    } else {                  // right block is new
      lnum_left = 0;
      if (in_left) {
        lnum_right = lnum + 2;
      } else {
        lnum_right = lnum + 1;
      }
    }
    dp_left->db_line_count = line_count_left;
    dp_right->db_line_count = line_count_right;

    /*
     * release the two data blocks
     * The new one (hp_new) already has a correct blocknumber.
     * The old one (hp, in ml_locked) gets a positive blocknumber if
     * we changed it and we are not editing a new file.
     */
    if (lines_moved || in_left) {
      buf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
    }
    if (!newfile && db_idx >= 0 && in_left) {
      buf->b_ml.ml_flags |= ML_LOCKED_POS;
    }
    mf_put(mfp, hp_new, true, false);

    /*
     * flush the old data block
     * set ml_locked_lineadd to 0, because the updating of the
     * pointer blocks is done below
     */
    lineadd = buf->b_ml.ml_locked_lineadd;
    buf->b_ml.ml_locked_lineadd = 0;
    (void)ml_find_line(buf, (linenr_T)0, ML_FLUSH);  // flush data block

    /*
     * update pointer blocks for the new data block
     */
    for (stack_idx = buf->b_ml.ml_stack_top - 1; stack_idx >= 0;
         --stack_idx) {
      ip = &(buf->b_ml.ml_stack[stack_idx]);
      pb_idx = ip->ip_index;
      if ((hp = mf_get(mfp, ip->ip_bnum, 1)) == NULL) {
        return FAIL;
      }
      pp = hp->bh_data;         // must be pointer block
      if (pp->pb_id != PTR_ID) {
        iemsg(_("E317: pointer block id wrong 3"));
        mf_put(mfp, hp, false, false);
        return FAIL;
      }
      /*
       * TODO: If the pointer block is full and we are adding at the end
       * try to insert in front of the next block
       */
      // block not full, add one entry
      if (pp->pb_count < pp->pb_count_max) {
        if (pb_idx + 1 < (int)pp->pb_count) {
          memmove(&pp->pb_pointer[pb_idx + 2],
                  &pp->pb_pointer[pb_idx + 1],
                  (size_t)(pp->pb_count - pb_idx - 1) * sizeof(PTR_EN));
        }
        ++pp->pb_count;
        pp->pb_pointer[pb_idx].pe_line_count = line_count_left;
        pp->pb_pointer[pb_idx].pe_bnum = bnum_left;
        pp->pb_pointer[pb_idx].pe_page_count = page_count_left;
        pp->pb_pointer[pb_idx + 1].pe_line_count = line_count_right;
        pp->pb_pointer[pb_idx + 1].pe_bnum = bnum_right;
        pp->pb_pointer[pb_idx + 1].pe_page_count = page_count_right;

        if (lnum_left != 0) {
          pp->pb_pointer[pb_idx].pe_old_lnum = lnum_left;
        }
        if (lnum_right != 0) {
          pp->pb_pointer[pb_idx + 1].pe_old_lnum = lnum_right;
        }

        mf_put(mfp, hp, true, false);
        buf->b_ml.ml_stack_top = stack_idx + 1;             // truncate stack

        if (lineadd) {
          --(buf->b_ml.ml_stack_top);
          // fix line count for rest of blocks in the stack
          ml_lineadd(buf, lineadd);
          // fix stack itself
          buf->b_ml.ml_stack[buf->b_ml.ml_stack_top].ip_high +=
            lineadd;
          ++(buf->b_ml.ml_stack_top);
        }

        /*
         * We are finished, break the loop here.
         */
        break;
      } else {                        // pointer block full
        /*
         * split the pointer block
         * allocate a new pointer block
         * move some of the pointer into the new block
         * prepare for updating the parent block
         */
        for (;;) {             // do this twice when splitting block 1
          hp_new = ml_new_ptr(mfp);
          if (hp_new == NULL) {             // TODO: try to fix tree
            return FAIL;
          }
          pp_new = hp_new->bh_data;

          if (hp->bh_bnum != 1) {
            break;
          }

          /*
           * if block 1 becomes full the tree is given an extra level
           * The pointers from block 1 are moved into the new block.
           * block 1 is updated to point to the new block
           * then continue to split the new block
           */
          memmove(pp_new, pp, (size_t)page_size);
          pp->pb_count = 1;
          pp->pb_pointer[0].pe_bnum = hp_new->bh_bnum;
          pp->pb_pointer[0].pe_line_count = buf->b_ml.ml_line_count;
          pp->pb_pointer[0].pe_old_lnum = 1;
          pp->pb_pointer[0].pe_page_count = 1;
          mf_put(mfp, hp, true, false);             // release block 1
          hp = hp_new;                          // new block is to be split
          pp = pp_new;
          CHECK(stack_idx != 0, _("stack_idx should be 0"));
          ip->ip_index = 0;
          ++stack_idx;                  // do block 1 again later
        }
        /*
         * move the pointers after the current one to the new block
         * If there are none, the new entry will be in the new block.
         */
        total_moved = pp->pb_count - pb_idx - 1;
        if (total_moved) {
          memmove(&pp_new->pb_pointer[0],
                  &pp->pb_pointer[pb_idx + 1],
                  (size_t)(total_moved) * sizeof(PTR_EN));
          pp_new->pb_count = total_moved;
          pp->pb_count -= total_moved - 1;
          pp->pb_pointer[pb_idx + 1].pe_bnum = bnum_right;
          pp->pb_pointer[pb_idx + 1].pe_line_count = line_count_right;
          pp->pb_pointer[pb_idx + 1].pe_page_count = page_count_right;
          if (lnum_right) {
            pp->pb_pointer[pb_idx + 1].pe_old_lnum = lnum_right;
          }
        } else {
          pp_new->pb_count = 1;
          pp_new->pb_pointer[0].pe_bnum = bnum_right;
          pp_new->pb_pointer[0].pe_line_count = line_count_right;
          pp_new->pb_pointer[0].pe_page_count = page_count_right;
          pp_new->pb_pointer[0].pe_old_lnum = lnum_right;
        }
        pp->pb_pointer[pb_idx].pe_bnum = bnum_left;
        pp->pb_pointer[pb_idx].pe_line_count = line_count_left;
        pp->pb_pointer[pb_idx].pe_page_count = page_count_left;
        if (lnum_left) {
          pp->pb_pointer[pb_idx].pe_old_lnum = lnum_left;
        }
        lnum_left = 0;
        lnum_right = 0;

        /*
         * recompute line counts
         */
        line_count_right = 0;
        for (i = 0; i < (int)pp_new->pb_count; ++i) {
          line_count_right += pp_new->pb_pointer[i].pe_line_count;
        }
        line_count_left = 0;
        for (i = 0; i < (int)pp->pb_count; ++i) {
          line_count_left += pp->pb_pointer[i].pe_line_count;
        }

        bnum_left = hp->bh_bnum;
        bnum_right = hp_new->bh_bnum;
        page_count_left = 1;
        page_count_right = 1;
        mf_put(mfp, hp, true, false);
        mf_put(mfp, hp_new, true, false);
      }
    }

    /*
     * Safety check: fallen out of for loop?
     */
    if (stack_idx < 0) {
      iemsg(_("E318: Updated too many blocks?"));
      buf->b_ml.ml_stack_top = 0;       // invalidate stack
    }
  }

  // The line was inserted below 'lnum'
  ml_updatechunk(buf, lnum + 1, (long)len, ML_CHNK_ADDLINE);
  return OK;
}

void ml_add_deleted_len(char_u *ptr, ssize_t len)
{
  ml_add_deleted_len_buf(curbuf, ptr, len);
}

void ml_add_deleted_len_buf(buf_T *buf, char_u *ptr, ssize_t len)
{
  if (inhibit_delete_count) {
    return;
  }
  if (len == -1) {
    len = STRLEN(ptr);
  }
  curbuf->deleted_bytes += len+1;
  curbuf->deleted_bytes2 += len+1;
  if (curbuf->update_need_codepoints) {
    mb_utflen(ptr, len, &curbuf->deleted_codepoints,
              &curbuf->deleted_codeunits);
    curbuf->deleted_codepoints++;  // NL char
    curbuf->deleted_codeunits++;
  }
}


int ml_replace(linenr_T lnum, char_u *line, bool copy)
{
  return ml_replace_buf(curbuf, lnum, line, copy);
}

// Replace line "lnum", with buffering, in current buffer.
//
// If "copy" is true, make a copy of the line, otherwise the line has been
// copied to allocated memory already.
// If "copy" is false the "line" may be freed to add text properties!
// Do not use it after calling ml_replace().
//
// Check: The caller of this function should probably also call
// changed_lines(), unless update_screen(NOT_VALID) is used.
//
// return FAIL for failure, OK otherwise
int ml_replace_buf(buf_T *buf, linenr_T lnum, char_u *line, bool copy)
{
  if (line == NULL) {           // just checking...
    return FAIL;
  }

  // When starting up, we might still need to create the memfile
  if (buf->b_ml.ml_mfp == NULL && open_buffer(false, NULL, 0) == FAIL) {
    return FAIL;
  }

  bool readlen = true;

  if (copy) {
    line = vim_strsave(line);
  }
  if (buf->b_ml.ml_line_lnum != lnum) {  // other line buffered
    ml_flush_line(buf);  // flush it
  } else if (buf->b_ml.ml_flags & ML_LINE_DIRTY) {  // same line allocated
    ml_add_deleted_len_buf(buf, buf->b_ml.ml_line_ptr, -1);
    readlen = false;  // already added the length

    xfree(buf->b_ml.ml_line_ptr);  // free it
  }

  if (readlen && kv_size(buf->update_callbacks)) {
    ml_add_deleted_len_buf(buf, ml_get_buf(buf, lnum, false), -1);
  }

  buf->b_ml.ml_line_ptr = line;
  buf->b_ml.ml_line_lnum = lnum;
  buf->b_ml.ml_flags = (buf->b_ml.ml_flags | ML_LINE_DIRTY) & ~ML_EMPTY;

  return OK;
}

/// Delete line `lnum` in the current buffer.
///
/// @note The caller of this function should probably also call
/// deleted_lines() after this.
///
/// @param message  Show "--No lines in buffer--" message.
/// @return FAIL for failure, OK otherwise
int ml_delete(linenr_T lnum, bool message)
{
  ml_flush_line(curbuf);
  return ml_delete_int(curbuf, lnum, message);
}

static int ml_delete_int(buf_T *buf, linenr_T lnum, bool message)
{
  bhdr_T *hp;
  memfile_T *mfp;
  DATA_BL *dp;
  PTR_BL *pp;
  infoptr_T *ip;
  int count;                // number of entries in block
  int idx;
  int stack_idx;
  int text_start;
  int line_start;
  long line_size;
  int i;

  if (lnum < 1 || lnum > buf->b_ml.ml_line_count) {
    return FAIL;
  }

  if (lowest_marked && lowest_marked > lnum) {
    lowest_marked--;
  }

  /*
   * If the file becomes empty the last line is replaced by an empty line.
   */
  if (buf->b_ml.ml_line_count == 1) {       // file becomes empty
    if (message) {
      set_keep_msg(_(no_lines_msg), 0);
    }

    i = ml_replace((linenr_T)1, (char_u *)"", true);
    buf->b_ml.ml_flags |= ML_EMPTY;

    return i;
  }

  /*
   * find the data block containing the line
   * This also fills the stack with the blocks from the root to the data block
   * This also releases any locked block.
   */
  mfp = buf->b_ml.ml_mfp;
  if (mfp == NULL) {
    return FAIL;
  }

  if ((hp = ml_find_line(buf, lnum, ML_DELETE)) == NULL) {
    return FAIL;
  }

  dp = hp->bh_data;
  // compute line count before the delete
  count = (long)(buf->b_ml.ml_locked_high)
          - (long)(buf->b_ml.ml_locked_low) + 2;
  idx = lnum - buf->b_ml.ml_locked_low;

  --buf->b_ml.ml_line_count;

  line_start = ((dp->db_index[idx]) & DB_INDEX_MASK);
  if (idx == 0) {               // first line in block, text at the end
    line_size = dp->db_txt_end - line_start;
  } else {
    line_size = ((dp->db_index[idx - 1]) & DB_INDEX_MASK) - line_start;
  }

  // Line should always have an NL char internally (represented as NUL),
  // even if 'noeol' is set.
  assert(line_size >= 1);
  ml_add_deleted_len_buf(buf, (char_u *)dp + line_start, line_size-1);

  /*
   * special case: If there is only one line in the data block it becomes empty.
   * Then we have to remove the entry, pointing to this data block, from the
   * pointer block. If this pointer block also becomes empty, we go up another
   * block, and so on, up to the root if necessary.
   * The line counts in the pointer blocks have already been adjusted by
   * ml_find_line().
   */
  if (count == 1) {
    mf_free(mfp, hp);           // free the data block
    buf->b_ml.ml_locked = NULL;

    for (stack_idx = buf->b_ml.ml_stack_top - 1; stack_idx >= 0;
         --stack_idx) {
      buf->b_ml.ml_stack_top = 0;           // stack is invalid when failing
      ip = &(buf->b_ml.ml_stack[stack_idx]);
      idx = ip->ip_index;
      if ((hp = mf_get(mfp, ip->ip_bnum, 1)) == NULL) {
        return FAIL;
      }
      pp = hp->bh_data;         // must be pointer block
      if (pp->pb_id != PTR_ID) {
        iemsg(_("E317: pointer block id wrong 4"));
        mf_put(mfp, hp, false, false);
        return FAIL;
      }
      count = --(pp->pb_count);
      if (count == 0) {             // the pointer block becomes empty!
        mf_free(mfp, hp);
      } else {
        if (count != idx) {             // move entries after the deleted one
          memmove(&pp->pb_pointer[idx], &pp->pb_pointer[idx + 1],
                  (size_t)(count - idx) * sizeof(PTR_EN));
        }
        mf_put(mfp, hp, true, false);

        buf->b_ml.ml_stack_top = stack_idx;             // truncate stack
        // fix line count for rest of blocks in the stack
        if (buf->b_ml.ml_locked_lineadd != 0) {
          ml_lineadd(buf, buf->b_ml.ml_locked_lineadd);
          buf->b_ml.ml_stack[buf->b_ml.ml_stack_top].ip_high +=
            buf->b_ml.ml_locked_lineadd;
        }
        ++(buf->b_ml.ml_stack_top);

        break;
      }
    }
    CHECK(stack_idx < 0, _("deleted block 1?"));
  } else {
    /*
     * delete the text by moving the next lines forwards
     */
    text_start = dp->db_txt_start;
    memmove((char *)dp + text_start + line_size,
            (char *)dp + text_start, (size_t)(line_start - text_start));

    /*
     * delete the index by moving the next indexes backwards
     * Adjust the indexes for the text movement.
     */
    for (i = idx; i < count - 1; ++i) {
      dp->db_index[i] = dp->db_index[i + 1] + line_size;
    }

    dp->db_free += line_size + INDEX_SIZE;
    dp->db_txt_start += line_size;
    --(dp->db_line_count);

    /*
     * mark the block dirty and make sure it is in the file (for recovery)
     */
    buf->b_ml.ml_flags |= (ML_LOCKED_DIRTY | ML_LOCKED_POS);
  }

  ml_updatechunk(buf, lnum, line_size, ML_CHNK_DELLINE);
  return OK;
}

/*
 * set the B_MARKED flag for line 'lnum'
 */
void ml_setmarked(linenr_T lnum)
{
  bhdr_T *hp;
  DATA_BL *dp;
  // invalid line number
  if (lnum < 1 || lnum > curbuf->b_ml.ml_line_count
      || curbuf->b_ml.ml_mfp == NULL) {
    return;                         // give error message?
  }
  if (lowest_marked == 0 || lowest_marked > lnum) {
    lowest_marked = lnum;
  }

  /*
   * find the data block containing the line
   * This also fills the stack with the blocks from the root to the data block
   * This also releases any locked block.
   */
  if ((hp = ml_find_line(curbuf, lnum, ML_FIND)) == NULL) {
    return;                 // give error message?
  }
  dp = hp->bh_data;
  dp->db_index[lnum - curbuf->b_ml.ml_locked_low] |= DB_MARKED;
  curbuf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
}

/*
 * find the first line with its B_MARKED flag set
 */
linenr_T ml_firstmarked(void)
{
  bhdr_T *hp;
  DATA_BL *dp;
  linenr_T lnum;
  int i;

  if (curbuf->b_ml.ml_mfp == NULL) {
    return (linenr_T)0;
  }

  /*
   * The search starts with lowest_marked line. This is the last line where
   * a mark was found, adjusted by inserting/deleting lines.
   */
  for (lnum = lowest_marked; lnum <= curbuf->b_ml.ml_line_count;) {
    /*
     * Find the data block containing the line.
     * This also fills the stack with the blocks from the root to the data
     * block This also releases any locked block.
     */
    if ((hp = ml_find_line(curbuf, lnum, ML_FIND)) == NULL) {
      return (linenr_T)0;                   // give error message?
    }
    dp = hp->bh_data;

    for (i = lnum - curbuf->b_ml.ml_locked_low;
         lnum <= curbuf->b_ml.ml_locked_high; ++i, ++lnum) {
      if ((dp->db_index[i]) & DB_MARKED) {
        (dp->db_index[i]) &= DB_INDEX_MASK;
        curbuf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
        lowest_marked = lnum + 1;
        return lnum;
      }
    }
  }

  return (linenr_T)0;
}

/*
 * clear all DB_MARKED flags
 */
void ml_clearmarked(void)
{
  bhdr_T *hp;
  DATA_BL *dp;
  linenr_T lnum;
  int i;

  if (curbuf->b_ml.ml_mfp == NULL) {        // nothing to do
    return;
  }

  /*
   * The search starts with line lowest_marked.
   */
  for (lnum = lowest_marked; lnum <= curbuf->b_ml.ml_line_count;) {
    /*
     * Find the data block containing the line.
     * This also fills the stack with the blocks from the root to the data
     * block and releases any locked block.
     */
    if ((hp = ml_find_line(curbuf, lnum, ML_FIND)) == NULL) {
      return;                   // give error message?
    }
    dp = hp->bh_data;

    for (i = lnum - curbuf->b_ml.ml_locked_low;
         lnum <= curbuf->b_ml.ml_locked_high; ++i, ++lnum) {
      if ((dp->db_index[i]) & DB_MARKED) {
        (dp->db_index[i]) &= DB_INDEX_MASK;
        curbuf->b_ml.ml_flags |= ML_LOCKED_DIRTY;
      }
    }
  }

  lowest_marked = 0;
}

size_t ml_flush_deleted_bytes(buf_T *buf, size_t *codepoints, size_t *codeunits)
{
  size_t ret = buf->deleted_bytes;
  *codepoints = buf->deleted_codepoints;
  *codeunits = buf->deleted_codeunits;
  buf->deleted_bytes = 0;
  buf->deleted_codepoints = 0;
  buf->deleted_codeunits = 0;
  return ret;
}

/*
 * flush ml_line if necessary
 */
static void ml_flush_line(buf_T *buf)
{
  bhdr_T *hp;
  DATA_BL *dp;
  linenr_T lnum;
  char_u *new_line;
  char_u *old_line;
  colnr_T new_len;
  int old_len;
  int extra;
  int idx;
  int start;
  int count;
  int i;
  static bool entered = false;

  if (buf->b_ml.ml_line_lnum == 0 || buf->b_ml.ml_mfp == NULL) {
    return;             // nothing to do
  }
  if (buf->b_ml.ml_flags & ML_LINE_DIRTY) {
    // This code doesn't work recursively.
    if (entered) {
      return;
    }
    entered = true;

    buf->flush_count++;

    lnum = buf->b_ml.ml_line_lnum;
    new_line = buf->b_ml.ml_line_ptr;

    hp = ml_find_line(buf, lnum, ML_FIND);
    if (hp == NULL) {
      siemsg(_("E320: Cannot find line %" PRId64), (int64_t)lnum);
    } else {
      dp = hp->bh_data;
      idx = lnum - buf->b_ml.ml_locked_low;
      start = ((dp->db_index[idx]) & DB_INDEX_MASK);
      old_line = (char_u *)dp + start;
      if (idx == 0) {           // line is last in block
        old_len = dp->db_txt_end - start;
      } else {  // text of previous line follows
        old_len = (dp->db_index[idx - 1] & DB_INDEX_MASK) - start;
      }
      new_len = (colnr_T)STRLEN(new_line) + 1;
      extra = new_len - old_len;            // negative if lines gets smaller

      /*
       * if new line fits in data block, replace directly
       */
      if ((int)dp->db_free >= extra) {
        // if the length changes and there are following lines
        count = buf->b_ml.ml_locked_high - buf->b_ml.ml_locked_low + 1;
        if (extra != 0 && idx < count - 1) {
          // move text of following lines
          memmove((char *)dp + dp->db_txt_start - extra,
                  (char *)dp + dp->db_txt_start,
                  (size_t)(start - dp->db_txt_start));

          // adjust pointers of this and following lines
          for (i = idx + 1; i < count; ++i) {
            dp->db_index[i] -= extra;
          }
        }
        dp->db_index[idx] -= extra;

        // adjust free space
        dp->db_free -= extra;
        dp->db_txt_start -= extra;

        // copy new line into the data block
        memmove(old_line - extra, new_line, (size_t)new_len);
        buf->b_ml.ml_flags |= (ML_LOCKED_DIRTY | ML_LOCKED_POS);
        // The else case is already covered by the insert and delete
        ml_updatechunk(buf, lnum, (long)extra, ML_CHNK_UPDLINE);
      } else {
        // Cannot do it in one data block: Delete and append.
        // Append first, because ml_delete_int() cannot delete the
        // last line in a buffer, which causes trouble for a buffer
        // that has only one line.
        // Don't forget to copy the mark!
        // How about handling errors???
        (void)ml_append_int(buf, lnum, new_line, new_len, false,
                            (dp->db_index[idx] & DB_MARKED));
        (void)ml_delete_int(buf, lnum, false);
      }
    }
    xfree(new_line);

    entered = false;
  }

  buf->b_ml.ml_line_lnum = 0;
  buf->b_ml.ml_line_offset = 0;
}

/*
 * create a new, empty, data block
 */
static bhdr_T *ml_new_data(memfile_T *mfp, bool negative, int page_count)
{
  assert(page_count >= 0);
  bhdr_T *hp = mf_new(mfp, negative, (unsigned)page_count);
  DATA_BL *dp = hp->bh_data;
  dp->db_id = DATA_ID;
  dp->db_txt_start = dp->db_txt_end = page_count * mfp->mf_page_size;
  dp->db_free = dp->db_txt_start - HEADER_SIZE;
  dp->db_line_count = 0;

  return hp;
}

/*
 * create a new, empty, pointer block
 */
static bhdr_T *ml_new_ptr(memfile_T *mfp)
{
  bhdr_T *hp = mf_new(mfp, false, 1);
  PTR_BL *pp = hp->bh_data;
  pp->pb_id = PTR_ID;
  pp->pb_count = 0;
  pp->pb_count_max = (mfp->mf_page_size - sizeof(PTR_BL)) / sizeof(PTR_EN) + 1;

  return hp;
}

/*
 * lookup line 'lnum' in a memline
 *
 *   action: if ML_DELETE or ML_INSERT the line count is updated while searching
 *           if ML_FLUSH only flush a locked block
 *           if ML_FIND just find the line
 *
 * If the block was found it is locked and put in ml_locked.
 * The stack is updated to lead to the locked block. The ip_high field in
 * the stack is updated to reflect the last line in the block AFTER the
 * insert or delete, also if the pointer block has not been updated yet. But
 * if ml_locked != NULL ml_locked_lineadd must be added to ip_high.
 *
 * return: NULL for failure, pointer to block header otherwise
 */
static bhdr_T *ml_find_line(buf_T *buf, linenr_T lnum, int action)
{
  DATA_BL *dp;
  PTR_BL *pp;
  infoptr_T *ip;
  bhdr_T *hp;
  memfile_T *mfp;
  linenr_T t;
  blocknr_T bnum, bnum2;
  int dirty;
  linenr_T low, high;
  int top;
  int page_count;
  int idx;

  mfp = buf->b_ml.ml_mfp;

  /*
   * If there is a locked block check if the wanted line is in it.
   * If not, flush and release the locked block.
   * Don't do this for ML_INSERT_SAME, because the stack need to be updated.
   * Don't do this for ML_FLUSH, because we want to flush the locked block.
   * Don't do this when 'swapfile' is reset, we want to load all the blocks.
   */
  if (buf->b_ml.ml_locked) {
    if (ML_SIMPLE(action)
        && buf->b_ml.ml_locked_low <= lnum
        && buf->b_ml.ml_locked_high >= lnum) {
      // remember to update pointer blocks and stack later
      if (action == ML_INSERT) {
        ++(buf->b_ml.ml_locked_lineadd);
        ++(buf->b_ml.ml_locked_high);
      } else if (action == ML_DELETE) {
        --(buf->b_ml.ml_locked_lineadd);
        --(buf->b_ml.ml_locked_high);
      }
      return buf->b_ml.ml_locked;
    }

    mf_put(mfp, buf->b_ml.ml_locked, buf->b_ml.ml_flags & ML_LOCKED_DIRTY,
           buf->b_ml.ml_flags & ML_LOCKED_POS);
    buf->b_ml.ml_locked = NULL;

    /*
     * If lines have been added or deleted in the locked block, need to
     * update the line count in pointer blocks.
     */
    if (buf->b_ml.ml_locked_lineadd != 0) {
      ml_lineadd(buf, buf->b_ml.ml_locked_lineadd);
    }
  }

  if (action == ML_FLUSH) {         // nothing else to do
    return NULL;
  }

  bnum = 1;                         // start at the root of the tree
  page_count = 1;
  low = 1;
  high = buf->b_ml.ml_line_count;

  if (action == ML_FIND) {      // first try stack entries
    for (top = buf->b_ml.ml_stack_top - 1; top >= 0; --top) {
      ip = &(buf->b_ml.ml_stack[top]);
      if (ip->ip_low <= lnum && ip->ip_high >= lnum) {
        bnum = ip->ip_bnum;
        low = ip->ip_low;
        high = ip->ip_high;
        buf->b_ml.ml_stack_top = top;           // truncate stack at prev entry
        break;
      }
    }
    if (top < 0) {
      buf->b_ml.ml_stack_top = 0;               // not found, start at the root
    }
  } else {  // ML_DELETE or ML_INSERT
    buf->b_ml.ml_stack_top = 0;         // start at the root
  }
  /*
   * search downwards in the tree until a data block is found
   */
  for (;;) {
    if ((hp = mf_get(mfp, bnum, page_count)) == NULL) {
      goto error_noblock;
    }

    /*
     * update high for insert/delete
     */
    if (action == ML_INSERT) {
      ++high;
    } else if (action == ML_DELETE) {
      --high;
    }

    dp = hp->bh_data;
    if (dp->db_id == DATA_ID) {         // data block
      buf->b_ml.ml_locked = hp;
      buf->b_ml.ml_locked_low = low;
      buf->b_ml.ml_locked_high = high;
      buf->b_ml.ml_locked_lineadd = 0;
      buf->b_ml.ml_flags &= ~(ML_LOCKED_DIRTY | ML_LOCKED_POS);
      return hp;
    }

    pp = (PTR_BL *)(dp);                // must be pointer block
    if (pp->pb_id != PTR_ID) {
      iemsg(_("E317: pointer block id wrong"));
      goto error_block;
    }

    top = ml_add_stack(buf);  // add new entry to stack
    ip = &(buf->b_ml.ml_stack[top]);
    ip->ip_bnum = bnum;
    ip->ip_low = low;
    ip->ip_high = high;
    ip->ip_index = -1;                  // index not known yet

    dirty = FALSE;
    for (idx = 0; idx < (int)pp->pb_count; ++idx) {
      t = pp->pb_pointer[idx].pe_line_count;
      CHECK(t == 0, _("pe_line_count is zero"));
      if ((low += t) > lnum) {
        ip->ip_index = idx;
        bnum = pp->pb_pointer[idx].pe_bnum;
        page_count = pp->pb_pointer[idx].pe_page_count;
        high = low - 1;
        low -= t;

        /*
         * a negative block number may have been changed
         */
        if (bnum < 0) {
          bnum2 = mf_trans_del(mfp, bnum);
          if (bnum != bnum2) {
            bnum = bnum2;
            pp->pb_pointer[idx].pe_bnum = bnum;
            dirty = TRUE;
          }
        }

        break;
      }
    }
    if (idx >= (int)pp->pb_count) {         // past the end: something wrong!
      if (lnum > buf->b_ml.ml_line_count) {
        siemsg(_("E322: line number out of range: %" PRId64 " past the end"),
               (int64_t)lnum - buf->b_ml.ml_line_count);
      } else {
        siemsg(_("E323: line count wrong in block %" PRId64), bnum);
      }
      goto error_block;
    }
    if (action == ML_DELETE) {
      pp->pb_pointer[idx].pe_line_count--;
      dirty = TRUE;
    } else if (action == ML_INSERT) {
      pp->pb_pointer[idx].pe_line_count++;
      dirty = TRUE;
    }
    mf_put(mfp, hp, dirty, false);
  }

error_block:
  mf_put(mfp, hp, false, false);
error_noblock:
  /*
   * If action is ML_DELETE or ML_INSERT we have to correct the tree for
   * the incremented/decremented line counts, because there won't be a line
   * inserted/deleted after all.
   */
  if (action == ML_DELETE) {
    ml_lineadd(buf, 1);
  } else if (action == ML_INSERT) {
    ml_lineadd(buf, -1);
  }
  buf->b_ml.ml_stack_top = 0;
  return NULL;
}

/*
 * add an entry to the info pointer stack
 *
 * return number of the new entry
 */
static int ml_add_stack(buf_T *buf)
{
  int top = buf->b_ml.ml_stack_top;

  // may have to increase the stack size
  if (top == buf->b_ml.ml_stack_size) {
    CHECK(top > 0, _("Stack size increases"));     // more than 5 levels???

    buf->b_ml.ml_stack_size += STACK_INCR;
    size_t new_size = sizeof(infoptr_T) * buf->b_ml.ml_stack_size;
    buf->b_ml.ml_stack = xrealloc(buf->b_ml.ml_stack, new_size);
  }

  buf->b_ml.ml_stack_top++;
  return top;
}

/*
 * Update the pointer blocks on the stack for inserted/deleted lines.
 * The stack itself is also updated.
 *
 * When an insert/delete line action fails, the line is not inserted/deleted,
 * but the pointer blocks have already been updated. That is fixed here by
 * walking through the stack.
 *
 * Count is the number of lines added, negative if lines have been deleted.
 */
static void ml_lineadd(buf_T *buf, int count)
{
  int idx;
  infoptr_T *ip;
  PTR_BL *pp;
  memfile_T *mfp = buf->b_ml.ml_mfp;
  bhdr_T *hp;

  for (idx = buf->b_ml.ml_stack_top - 1; idx >= 0; --idx) {
    ip = &(buf->b_ml.ml_stack[idx]);
    if ((hp = mf_get(mfp, ip->ip_bnum, 1)) == NULL) {
      break;
    }
    pp = hp->bh_data;       // must be pointer block
    if (pp->pb_id != PTR_ID) {
      mf_put(mfp, hp, false, false);
      iemsg(_("E317: pointer block id wrong 2"));
      break;
    }
    pp->pb_pointer[ip->ip_index].pe_line_count += count;
    ip->ip_high += count;
    mf_put(mfp, hp, true, false);
  }
}

#if defined(HAVE_READLINK)
/*
 * Resolve a symlink in the last component of a file name.
 * Note that f_resolve() does it for every part of the path, we don't do that
 * here.
 * If it worked returns OK and the resolved link in "buf[MAXPATHL]".
 * Otherwise returns FAIL.
 */
int resolve_symlink(const char_u *fname, char_u *buf)
{
  char_u tmp[MAXPATHL];
  int ret;
  int depth = 0;

  if (fname == NULL) {
    return FAIL;
  }

  // Put the result so far in tmp[], starting with the original name.
  STRLCPY(tmp, fname, MAXPATHL);

  for (;;) {
    // Limit symlink depth to 100, catch recursive loops.
    if (++depth == 100) {
      semsg(_("E773: Symlink loop for \"%s\""), fname);
      return FAIL;
    }

    ret = readlink((char *)tmp, (char *)buf, MAXPATHL - 1);
    if (ret <= 0) {
      if (errno == EINVAL || errno == ENOENT) {
        // Found non-symlink or not existing file, stop here.
        // When at the first level use the unmodified name, skip the
        // call to vim_FullName().
        if (depth == 1) {
          return FAIL;
        }

        // Use the resolved name in tmp[].
        break;
      }

      // There must be some error reading links, use original name.
      return FAIL;
    }
    buf[ret] = NUL;

    // Check whether the symlink is relative or absolute.
    // If it's relative, build a new path based on the directory
    // portion of the filename (if any) and the path the symlink
    // points to.
    if (path_is_absolute(buf)) {
      STRCPY(tmp, buf);
    } else {
      char_u *tail = path_tail(tmp);
      if (STRLEN(tail) + STRLEN(buf) >= MAXPATHL) {
        return FAIL;
      }
      STRCPY(tail, buf);
    }
  }

  /*
   * Try to resolve the full name of the file so that the swapfile name will
   * be consistent even when opening a relative symlink from different
   * working directories.
   */
  return vim_FullName((char *)tmp, (char *)buf, MAXPATHL, TRUE);
}
#endif

/*
 * Make swap file name out of the file name and a directory name.
 * Returns pointer to allocated memory or NULL.
 */
char_u *makeswapname(char_u *fname, char_u *ffname, buf_T *buf, char_u *dir_name)
{
  char_u *r, *s;
  char_u *fname_res = fname;
#ifdef HAVE_READLINK
  char_u fname_buf[MAXPATHL];

  // Expand symlink in the file name, so that we put the swap file with the
  // actual file instead of with the symlink.
  if (resolve_symlink(fname, fname_buf) == OK) {
    fname_res = fname_buf;
  }
#endif
  int len = (int)STRLEN(dir_name);

  s = dir_name + len;
  if (after_pathsep((char *)dir_name, (char *)s)
      && len > 1
      && s[-1] == s[-2]) {  // Ends with '//', Use Full path
    r = NULL;
    s = (char_u *)make_percent_swname((char *)dir_name, (char *)fname_res);
    if (s != NULL) {
      r = (char_u *)modname((char *)s, ".swp", false);
      xfree(s);
    }
    return r;
  }

  // Prepend a '.' to the swap file name for the current directory.
  r = (char_u *)modname((char *)fname_res, ".swp",
                        dir_name[0] == '.' && dir_name[1] == NUL);
  if (r == NULL) {          // out of memory
    return NULL;
  }

  s = get_file_in_dir(r, dir_name);
  xfree(r);
  return s;
}

/// Get file name to use for swap file or backup file.
/// Use the name of the edited file "fname" and an entry in the 'dir' or 'bdir'
/// option "dname".
/// - If "dname" is ".", return "fname" (swap file in dir of file).
/// - If "dname" starts with "./", insert "dname" in "fname" (swap file
///   relative to dir of file).
/// - Otherwise, prepend "dname" to the tail of "fname" (swap file in specific
///   dir).
///
/// The return value is an allocated string and can be NULL.
///
/// @param dname  don't use "dirname", it is a global for Alpha
char_u *get_file_in_dir(char_u *fname, char_u *dname)
{
  char_u *t;
  char_u *tail;
  char_u *retval;
  int save_char;

  tail = path_tail(fname);

  if (dname[0] == '.' && dname[1] == NUL) {
    retval = vim_strsave(fname);
  } else if (dname[0] == '.' && vim_ispathsep(dname[1])) {
    if (tail == fname) {            // no path before file name
      retval = (char_u *)concat_fnames((char *)dname + 2, (char *)tail, TRUE);
    } else {
      save_char = *tail;
      *tail = NUL;
      t = (char_u *)concat_fnames((char *)fname, (char *)dname + 2, TRUE);
      *tail = save_char;
      retval = (char_u *)concat_fnames((char *)t, (char *)tail, TRUE);
      xfree(t);
    }
  } else {
    retval = (char_u *)concat_fnames((char *)dname, (char *)tail, TRUE);
  }

  return retval;
}


/// Print the ATTENTION message: info about an existing swap file.
///
/// @param buf  buffer being edited
/// @param fname  swap file name
static void attention_message(buf_T *buf, char_u *fname)
{
  assert(buf->b_fname != NULL);

  ++no_wait_return;
  (void)emsg(_("E325: ATTENTION"));
  msg_puts(_("\nFound a swap file by the name \""));
  msg_home_replace(fname);
  msg_puts("\"\n");
  const time_t swap_mtime = swapfile_info(fname);
  msg_puts(_("While opening file \""));
  msg_outtrans(buf->b_fname);
  msg_puts("\"\n");
  FileInfo file_info;
  if (!os_fileinfo((char *)buf->b_fname, &file_info)) {
    msg_puts(_("      CANNOT BE FOUND"));
  } else {
    msg_puts(_("             dated: "));
    time_t x = file_info.stat.st_mtim.tv_sec;
    char ctime_buf[50];
    msg_puts(os_ctime_r(&x, ctime_buf, sizeof(ctime_buf)));
    if (swap_mtime != 0 && x > swap_mtime) {
      msg_puts(_("      NEWER than swap file!\n"));
    }
  }
  // Some of these messages are long to allow translation to
  // other languages.
  msg_puts(_("\n(1) Another program may be editing the same file.  If this is"
             " the case,\n    be careful not to end up with two different"
             " instances of the same\n    file when making changes."
             "  Quit, or continue with caution.\n"));
  msg_puts(_("(2) An edit session for this file crashed.\n"));
  msg_puts(_("    If this is the case, use \":recover\" or \"vim -r "));
  msg_outtrans(buf->b_fname);
  msg_puts(_("\"\n    to recover the changes (see \":help recovery\").\n"));
  msg_puts(_("    If you did this already, delete the swap file \""));
  msg_outtrans(fname);
  msg_puts(_("\"\n    to avoid this message.\n"));
  cmdline_row = msg_row;
  --no_wait_return;
}


/*
 * Trigger the SwapExists autocommands.
 * Returns a value for equivalent to do_dialog() (see below):
 * 0: still need to ask for a choice
 * 1: open read-only
 * 2: edit anyway
 * 3: recover
 * 4: delete it
 * 5: quit
 * 6: abort
 */
static int do_swapexists(buf_T *buf, char_u *fname)
{
  set_vim_var_string(VV_SWAPNAME, (char *)fname, -1);
  set_vim_var_string(VV_SWAPCHOICE, NULL, -1);

  // Trigger SwapExists autocommands with <afile> set to the file being
  // edited.  Disallow changing directory here.
  allbuf_lock++;
  apply_autocmds(EVENT_SWAPEXISTS, buf->b_fname, NULL, false, NULL);
  allbuf_lock--;

  set_vim_var_string(VV_SWAPNAME, NULL, -1);

  switch (*get_vim_var_str(VV_SWAPCHOICE)) {
  case 'o':
    return 1;
  case 'e':
    return 2;
  case 'r':
    return 3;
  case 'd':
    return 4;
  case 'q':
    return 5;
  case 'a':
    return 6;
  }

  return 0;
}

/// Find out what name to use for the swap file for buffer 'buf'.
///
/// Several names are tried to find one that does not exist. Last directory in
/// option is automatically created.
///
/// @note If BASENAMELEN is not correct, you will get error messages for
///   not being able to open the swap or undo file.
/// @note May trigger SwapExists autocmd, pointers may change!
///
/// @param[in]  buf  Buffer for which swap file names needs to be found.
/// @param[in,out]  dirp  Pointer to a list of directories. When out of memory,
///                       is set to NULL. Is advanced to the next directory in
///                       the list otherwise.
/// @param[in]  old_fname  Allowed existing swap file name. Except for this
///                        case, name of the non-existing file is used.
/// @param[in,out]  found_existing_dir  If points to true, then new directory
///                                     for swap file is not created. At first
///                                     findswapname() call this argument must
///                                     point to false. This parameter may only
///                                     be set to true by this function, it is
///                                     never set to false.
///
/// @return [allocated] Name of the swap file.
static char *findswapname(buf_T *buf, char **dirp, char *old_fname, bool *found_existing_dir)
  FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_ARG(1, 2, 4)
{
  char *fname;
  size_t n;
  char *dir_name;
  char *buf_fname = (char *)buf->b_fname;

  /*
   * Isolate a directory name from *dirp and put it in dir_name.
   * First allocate some memory to put the directory name in.
   */
  const size_t dir_len = strlen(*dirp) + 1;
  dir_name = xmalloc(dir_len);
  (void)copy_option_part((char_u **)dirp, (char_u *)dir_name, dir_len, ",");

  /*
   * we try different names until we find one that does not exist yet
   */
  fname = (char *)makeswapname((char_u *)buf_fname, buf->b_ffname, buf,
                               (char_u *)dir_name);

  for (;;) {
    if (fname == NULL) {        // must be out of memory
      break;
    }
    if ((n = strlen(fname)) == 0) {        // safety check
      XFREE_CLEAR(fname);
      break;
    }
    // check if the swapfile already exists
    // Extra security check: When a swap file is a symbolic link, this
    // is most likely a symlink attack.
    FileInfo file_info;
    bool file_or_link_found = os_fileinfo_link(fname, &file_info);
    if (!file_or_link_found) {
      break;
    }

    // A file name equal to old_fname is OK to use.
    if (old_fname != NULL && fnamecmp(fname, old_fname) == 0) {
      break;
    }

    // get here when file already exists
    if (fname[n - 2] == 'w' && fname[n - 1] == 'p') {   // first try
      // If we get here the ".swp" file really exists.
      // Give an error message, unless recovering, no file name, we are
      // viewing a help file or when the path of the file is different
      // (happens when all .swp files are in one directory).
      if (!recoverymode && buf_fname != NULL
          && !buf->b_help && !(buf->b_flags & BF_DUMMY)) {
        int fd;
        struct block0 b0;
        int differ = FALSE;

        // Try to read block 0 from the swap file to get the original
        // file name (and inode number).
        fd = os_open(fname, O_RDONLY, 0);
        if (fd >= 0) {
          if (read_eintr(fd, &b0, sizeof(b0)) == sizeof(b0)) {
            // If the swapfile has the same directory as the
            // buffer don't compare the directory names, they can
            // have a different mountpoint.
            if (b0.b0_flags & B0_SAME_DIR) {
              if (fnamecmp(path_tail(buf->b_ffname),
                           path_tail(b0.b0_fname)) != 0
                  || !same_directory((char_u *)fname, buf->b_ffname)) {
                // Symlinks may point to the same file even
                // when the name differs, need to check the
                // inode too.
                expand_env(b0.b0_fname, NameBuff, MAXPATHL);
                if (fnamecmp_ino(buf->b_ffname, NameBuff,
                                 char_to_long(b0.b0_ino))) {
                  differ = TRUE;
                }
              }
            } else {
              // The name in the swap file may be
              // "~user/path/file".  Expand it first.
              expand_env(b0.b0_fname, NameBuff, MAXPATHL);
              if (fnamecmp_ino(buf->b_ffname, NameBuff,
                               char_to_long(b0.b0_ino))) {
                differ = TRUE;
              }
            }
          }
          close(fd);
        }

        // give the ATTENTION message when there is an old swap file
        // for the current file, and the buffer was not recovered.
        if (differ == false && !(curbuf->b_flags & BF_RECOVERED)
            && vim_strchr(p_shm, SHM_ATTENTION) == NULL) {
          int choice = 0;

          process_still_running = false;
          // It's safe to delete the swap file if all these are true:
          // - the edited file exists
          // - the swap file has no changes and looks OK
          if (os_path_exists(buf->b_fname) && swapfile_unchanged(fname)) {
            choice = 4;
            if (p_verbose > 0) {
              verb_msg(_("Found a swap file that is not useful, deleting it"));
            }
          }

          // If there is a SwapExists autocommand and we can handle the
          // response, trigger it.  It may return 0 to ask the user anyway.
          if (choice == 0
              && swap_exists_action != SEA_NONE
              && has_autocmd(EVENT_SWAPEXISTS, (char_u *)buf_fname, buf)) {
            choice = do_swapexists(buf, (char_u *)fname);
          }

          if (choice == 0) {
            // Show info about the existing swap file.
            attention_message(buf, (char_u *)fname);

            // We don't want a 'q' typed at the more-prompt
            // interrupt loading a file.
            got_int = false;

            // If vimrc has "simalt ~x" we don't want it to
            // interfere with the prompt here.
            flush_buffers(FLUSH_TYPEAHEAD);
          }

          if (swap_exists_action != SEA_NONE && choice == 0) {
            const char *const sw_msg_1 = _("Swap file \"");
            const char *const sw_msg_2 = _("\" already exists!");

            const size_t fname_len = strlen(fname);
            const size_t sw_msg_1_len = strlen(sw_msg_1);
            const size_t sw_msg_2_len = strlen(sw_msg_2);

            const size_t name_len = sw_msg_1_len + fname_len + sw_msg_2_len + 5;

            char *const name = xmalloc(name_len);
            memcpy(name, sw_msg_1, sw_msg_1_len + 1);
            home_replace(NULL, (char_u *)fname, (char_u *)&name[sw_msg_1_len],
                         fname_len, true);
            xstrlcat(name, sw_msg_2, name_len);
            choice = do_dialog(VIM_WARNING, (char_u *)_("VIM - ATTENTION"),
                               (char_u *)name,
                               process_still_running
                               ? (char_u *)_("&Open Read-Only\n&Edit anyway\n&Recover"
                                             "\n&Quit\n&Abort") :
                               (char_u *)_("&Open Read-Only\n&Edit anyway\n&Recover"
                                           "\n&Delete it\n&Quit\n&Abort"),
                               1, NULL, false);

            if (process_still_running && choice >= 4) {
              choice++;                 // Skip missing "Delete it" button.
            }
            xfree(name);

            // pretend screen didn't scroll, need redraw anyway
            msg_reset_scroll();
          }

          if (choice > 0) {
            switch (choice) {
            case 1:
              buf->b_p_ro = TRUE;
              break;
            case 2:
              break;
            case 3:
              swap_exists_action = SEA_RECOVER;
              break;
            case 4:
              os_remove(fname);
              break;
            case 5:
              swap_exists_action = SEA_QUIT;
              break;
            case 6:
              swap_exists_action = SEA_QUIT;
              got_int = TRUE;
              break;
            }

            // If the file was deleted this fname can be used.
            if (!os_path_exists((char_u *)fname)) {
              break;
            }
          } else {
            msg_puts("\n");
            if (msg_silent == 0) {
              // call wait_return() later
              need_wait_return = true;
            }
          }
        }
      }
    }

    /*
     * Change the ".swp" extension to find another file that can be used.
     * First decrement the last char: ".swo", ".swn", etc.
     * If that still isn't enough decrement the last but one char: ".svz"
     * Can happen when editing many "No Name" buffers.
     */
    if (fname[n - 1] == 'a') {          // ".s?a"
      if (fname[n - 2] == 'a') {        // ".saa": tried enough, give up
        emsg(_("E326: Too many swap files found"));
        XFREE_CLEAR(fname);
        break;
      }
      --fname[n - 2];                   // ".svz", ".suz", etc.
      fname[n - 1] = 'z' + 1;
    }
    --fname[n - 1];                     // ".swo", ".swn", etc.
  }

  if (os_isdir((char_u *)dir_name)) {
    *found_existing_dir = true;
  } else if (!*found_existing_dir && **dirp == NUL) {
    int ret;
    char *failed_dir;
    if ((ret = os_mkdir_recurse(dir_name, 0755, &failed_dir)) != 0) {
      semsg(_("E303: Unable to create directory \"%s\" for swap file, "
              "recovery impossible: %s"),
            failed_dir, os_strerror(ret));
      xfree(failed_dir);
    }
  }

  xfree(dir_name);
  return fname;
}

static int b0_magic_wrong(ZERO_BL *b0p)
{
  return b0p->b0_magic_long != (long)B0_MAGIC_LONG
         || b0p->b0_magic_int != (int)B0_MAGIC_INT
         || b0p->b0_magic_short != (short)B0_MAGIC_SHORT
         || b0p->b0_magic_char != B0_MAGIC_CHAR;
}

/// Compare current file name with file name from swap file.
/// Try to use inode numbers when possible.
/// Return non-zero when files are different.
///
/// When comparing file names a few things have to be taken into consideration:
/// - When working over a network the full path of a file depends on the host.
///   We check the inode number if possible.  It is not 100% reliable though,
///   because the device number cannot be used over a network.
/// - When a file does not exist yet (editing a new file) there is no inode
///   number.
/// - The file name in a swap file may not be valid on the current host.  The
///   "~user" form is used whenever possible to avoid this.
///
/// This is getting complicated, let's make a table:
///
///              ino_c  ino_s  fname_c  fname_s  differ =
///
/// both files exist -> compare inode numbers:
///              != 0   != 0     X        X      ino_c != ino_s
///
/// inode number(s) unknown, file names available -> compare file names
///              == 0    X       OK       OK     fname_c != fname_s
///               X     == 0     OK       OK     fname_c != fname_s
///
/// current file doesn't exist, file for swap file exist, file name(s) not
/// available -> probably different
///              == 0   != 0    FAIL      X      TRUE
///              == 0   != 0     X       FAIL    TRUE
///
/// current file exists, inode for swap unknown, file name(s) not
/// available -> probably different
///              != 0   == 0    FAIL      X      TRUE
///              != 0   == 0     X       FAIL    TRUE
///
/// current file doesn't exist, inode for swap unknown, one file name not
/// available -> probably different
///              == 0   == 0    FAIL      OK     TRUE
///              == 0   == 0     OK      FAIL    TRUE
///
/// current file doesn't exist, inode for swap unknown, both file names not
/// available -> compare file names
///              == 0   == 0    FAIL     FAIL    fname_c != fname_s
///
/// Only the last 32 bits of the inode will be used. This can't be changed
/// without making the block 0 incompatible with 32 bit versions.
///
/// @param fname_c  current file name
/// @param fname_s  file name from swap file
static bool fnamecmp_ino(char_u *fname_c, char_u *fname_s, long ino_block0)
{
  uint64_t ino_c = 0;               // ino of current file
  uint64_t ino_s;                   // ino of file from swap file
  char_u buf_c[MAXPATHL];           // full path of fname_c
  char_u buf_s[MAXPATHL];           // full path of fname_s
  int retval_c;                     // flag: buf_c valid
  int retval_s;                     // flag: buf_s valid

  FileInfo file_info;
  if (os_fileinfo((char *)fname_c, &file_info)) {
    ino_c = os_fileinfo_inode(&file_info);
  }

  /*
   * First we try to get the inode from the file name, because the inode in
   * the swap file may be outdated.  If that fails (e.g. this path is not
   * valid on this machine), use the inode from block 0.
   */
  if (os_fileinfo((char *)fname_s, &file_info)) {
    ino_s = os_fileinfo_inode(&file_info);
  } else {
    ino_s = (uint64_t)ino_block0;
  }

  if (ino_c && ino_s) {
    return ino_c != ino_s;
  }

  /*
   * One of the inode numbers is unknown, try a forced vim_FullName() and
   * compare the file names.
   */
  retval_c = vim_FullName((char *)fname_c, (char *)buf_c, MAXPATHL, TRUE);
  retval_s = vim_FullName((char *)fname_s, (char *)buf_s, MAXPATHL, TRUE);
  if (retval_c == OK && retval_s == OK) {
    return STRCMP(buf_c, buf_s) != 0;
  }

  /*
   * Can't compare inodes or file names, guess that the files are different,
   * unless both appear not to exist at all, then compare with the file name
   * in the swap file.
   */
  if (ino_s == 0 && ino_c == 0 && retval_c == FAIL && retval_s == FAIL) {
    return STRCMP(fname_c, fname_s) != 0;
  }
  return true;
}

/*
 * Move a long integer into a four byte character array.
 * Used for machine independency in block zero.
 */
static void long_to_char(long n, char_u *s)
{
  s[0] = (char_u)(n & 0xff);
  n = (unsigned)n >> 8;
  s[1] = (char_u)(n & 0xff);
  n = (unsigned)n >> 8;
  s[2] = (char_u)(n & 0xff);
  n = (unsigned)n >> 8;
  s[3] = (char_u)(n & 0xff);
}

static long char_to_long(char_u *s)
{
  long retval;

  retval = s[3];
  retval <<= 8;
  retval |= s[2];
  retval <<= 8;
  retval |= s[1];
  retval <<= 8;
  retval |= s[0];

  return retval;
}

/*
 * Set the flags in the first block of the swap file:
 * - file is modified or not: buf->b_changed
 * - 'fileformat'
 * - 'fileencoding'
 */
void ml_setflags(buf_T *buf)
{
  bhdr_T *hp;
  ZERO_BL *b0p;

  if (!buf->b_ml.ml_mfp) {
    return;
  }
  for (hp = buf->b_ml.ml_mfp->mf_used_last; hp != NULL; hp = hp->bh_prev) {
    if (hp->bh_bnum == 0) {
      b0p = hp->bh_data;
      b0p->b0_dirty = buf->b_changed ? B0_DIRTY : 0;
      b0p->b0_flags = (b0p->b0_flags & ~B0_FF_MASK)
                      | (get_fileformat(buf) + 1);
      add_b0_fenc(b0p, buf);
      hp->bh_flags |= BH_DIRTY;
      mf_sync(buf->b_ml.ml_mfp, MFS_ZERO);
      break;
    }
  }
}

#define MLCS_MAXL 800   // max no of lines in chunk
#define MLCS_MINL 400   // should be half of MLCS_MAXL

/*
 * Keep information for finding byte offset of a line, updtype may be one of:
 * ML_CHNK_ADDLINE: Add len to parent chunk, possibly splitting it
 *         Careful: ML_CHNK_ADDLINE may cause ml_find_line() to be called.
 * ML_CHNK_DELLINE: Subtract len from parent chunk, possibly deleting it
 * ML_CHNK_UPDLINE: Add len to parent chunk, as a signed entity.
 */
static void ml_updatechunk(buf_T *buf, linenr_T line, long len, int updtype)
{
  static buf_T *ml_upd_lastbuf = NULL;
  static linenr_T ml_upd_lastline;
  static linenr_T ml_upd_lastcurline;
  static int ml_upd_lastcurix;

  linenr_T curline = ml_upd_lastcurline;
  int curix = ml_upd_lastcurix;
  long size;
  chunksize_T *curchnk;
  int rest;
  bhdr_T *hp;
  DATA_BL *dp;

  if (buf->b_ml.ml_usedchunks == -1 || len == 0) {
    return;
  }
  if (buf->b_ml.ml_chunksize == NULL) {
    buf->b_ml.ml_chunksize = xmalloc(sizeof(chunksize_T) * 100);
    buf->b_ml.ml_numchunks = 100;
    buf->b_ml.ml_usedchunks = 1;
    buf->b_ml.ml_chunksize[0].mlcs_numlines = 1;
    buf->b_ml.ml_chunksize[0].mlcs_totalsize = 1;
  }

  if (updtype == ML_CHNK_UPDLINE && buf->b_ml.ml_line_count == 1) {
    /*
     * First line in empty buffer from ml_flush_line() -- reset
     */
    buf->b_ml.ml_usedchunks = 1;
    buf->b_ml.ml_chunksize[0].mlcs_numlines = 1;
    buf->b_ml.ml_chunksize[0].mlcs_totalsize =
      (long)STRLEN(buf->b_ml.ml_line_ptr) + 1;
    return;
  }

  /*
   * Find chunk that our line belongs to, curline will be at start of the
   * chunk.
   */
  if (buf != ml_upd_lastbuf || line != ml_upd_lastline + 1
      || updtype != ML_CHNK_ADDLINE) {
    for (curline = 1, curix = 0;
         curix < buf->b_ml.ml_usedchunks - 1
         && line >= curline +
         buf->b_ml.ml_chunksize[curix].mlcs_numlines;
         curix++) {
      curline += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    }
  } else if (curix < buf->b_ml.ml_usedchunks - 1
             && line >= curline + buf->b_ml.ml_chunksize[curix].mlcs_numlines) {
    // Adjust cached curix & curline
    curline += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    curix++;
  }
  curchnk = buf->b_ml.ml_chunksize + curix;

  if (updtype == ML_CHNK_DELLINE) {
    len = -len;
  }
  curchnk->mlcs_totalsize += len;
  if (updtype == ML_CHNK_ADDLINE) {
    curchnk->mlcs_numlines++;

    // May resize here so we don't have to do it in both cases below
    if (buf->b_ml.ml_usedchunks + 1 >= buf->b_ml.ml_numchunks) {
      buf->b_ml.ml_numchunks = buf->b_ml.ml_numchunks * 3 / 2;
      buf->b_ml.ml_chunksize = xrealloc(buf->b_ml.ml_chunksize,
                                        sizeof(chunksize_T) * buf->b_ml.ml_numchunks);
    }

    if (buf->b_ml.ml_chunksize[curix].mlcs_numlines >= MLCS_MAXL) {
      int count;                    // number of entries in block
      int idx;
      int text_end;
      int linecnt;

      memmove(buf->b_ml.ml_chunksize + curix + 1,
              buf->b_ml.ml_chunksize + curix,
              (buf->b_ml.ml_usedchunks - curix) *
              sizeof(chunksize_T));
      // Compute length of first half of lines in the split chunk
      size = 0;
      linecnt = 0;
      while (curline < buf->b_ml.ml_line_count
             && linecnt < MLCS_MINL) {
        if ((hp = ml_find_line(buf, curline, ML_FIND)) == NULL) {
          buf->b_ml.ml_usedchunks = -1;
          return;
        }
        dp = hp->bh_data;
        count = (long)(buf->b_ml.ml_locked_high) -
                (long)(buf->b_ml.ml_locked_low) + 1;
        idx = curline - buf->b_ml.ml_locked_low;
        curline = buf->b_ml.ml_locked_high + 1;
        if (idx == 0) {      // first line in block, text at the end
          text_end = dp->db_txt_end;
        } else {
          text_end = ((dp->db_index[idx - 1]) & DB_INDEX_MASK);
        }
        // Compute index of last line to use in this MEMLINE
        rest = count - idx;
        if (linecnt + rest > MLCS_MINL) {
          idx += MLCS_MINL - linecnt - 1;
          linecnt = MLCS_MINL;
        } else {
          idx = count - 1;
          linecnt += rest;
        }
        size += text_end - ((dp->db_index[idx]) & DB_INDEX_MASK);
      }
      buf->b_ml.ml_chunksize[curix].mlcs_numlines = linecnt;
      buf->b_ml.ml_chunksize[curix + 1].mlcs_numlines -= linecnt;
      buf->b_ml.ml_chunksize[curix].mlcs_totalsize = size;
      buf->b_ml.ml_chunksize[curix + 1].mlcs_totalsize -= size;
      buf->b_ml.ml_usedchunks++;
      ml_upd_lastbuf = NULL;         // Force recalc of curix & curline
      return;
    } else if (buf->b_ml.ml_chunksize[curix].mlcs_numlines >= MLCS_MINL
               && curix == buf->b_ml.ml_usedchunks - 1
               && buf->b_ml.ml_line_count - line <= 1) {
      /*
       * We are in the last chunk and it is cheap to crate a new one
       * after this. Do it now to avoid the loop above later on
       */
      curchnk = buf->b_ml.ml_chunksize + curix + 1;
      buf->b_ml.ml_usedchunks++;
      if (line == buf->b_ml.ml_line_count) {
        curchnk->mlcs_numlines = 0;
        curchnk->mlcs_totalsize = 0;
      } else {
        /*
         * Line is just prior to last, move count for last
         * This is the common case  when loading a new file
         */
        hp = ml_find_line(buf, buf->b_ml.ml_line_count, ML_FIND);
        if (hp == NULL) {
          buf->b_ml.ml_usedchunks = -1;
          return;
        }
        dp = hp->bh_data;
        if (dp->db_line_count == 1) {
          rest = dp->db_txt_end - dp->db_txt_start;
        } else {
          rest =
            ((dp->db_index[dp->db_line_count - 2]) & DB_INDEX_MASK)
            - dp->db_txt_start;
        }
        curchnk->mlcs_totalsize = rest;
        curchnk->mlcs_numlines = 1;
        curchnk[-1].mlcs_totalsize -= rest;
        curchnk[-1].mlcs_numlines -= 1;
      }
    }
  } else if (updtype == ML_CHNK_DELLINE) {
    curchnk->mlcs_numlines--;
    ml_upd_lastbuf = NULL;       // Force recalc of curix & curline
    if (curix < (buf->b_ml.ml_usedchunks - 1)
        && (curchnk->mlcs_numlines + curchnk[1].mlcs_numlines)
        <= MLCS_MINL) {
      curix++;
      curchnk = buf->b_ml.ml_chunksize + curix;
    } else if (curix == 0 && curchnk->mlcs_numlines <= 0) {
      buf->b_ml.ml_usedchunks--;
      memmove(buf->b_ml.ml_chunksize, buf->b_ml.ml_chunksize + 1,
              buf->b_ml.ml_usedchunks * sizeof(chunksize_T));
      return;
    } else if (curix == 0 || (curchnk->mlcs_numlines > 10
                              && (curchnk->mlcs_numlines +
                                  curchnk[-1].mlcs_numlines)
                              > MLCS_MINL)) {
      return;
    }

    // Collapse chunks
    curchnk[-1].mlcs_numlines += curchnk->mlcs_numlines;
    curchnk[-1].mlcs_totalsize += curchnk->mlcs_totalsize;
    buf->b_ml.ml_usedchunks--;
    if (curix < buf->b_ml.ml_usedchunks) {
      memmove(buf->b_ml.ml_chunksize + curix,
              buf->b_ml.ml_chunksize + curix + 1,
              (buf->b_ml.ml_usedchunks - curix) *
              sizeof(chunksize_T));
    }
    return;
  }
  ml_upd_lastbuf = buf;
  ml_upd_lastline = line;
  ml_upd_lastcurline = curline;
  ml_upd_lastcurix = curix;
}

/// Find offset for line or line with offset.
///
/// @param buf buffer to use
/// @param lnum if > 0, find offset of lnum, return offset
///             if == 0, return line with offset *offp
/// @param offp offset to use to find line, store remaining column offset
///             Should be NULL when getting offset of line
/// @param no_ff ignore 'fileformat' option, always use one byte for NL.
///
/// @return -1 if information is not available
long ml_find_line_or_offset(buf_T *buf, linenr_T lnum, long *offp, bool no_ff)
{
  linenr_T curline;
  int curix;
  long size;
  bhdr_T *hp;
  DATA_BL *dp;
  int count;                    // number of entries in block
  int idx;
  int start_idx;
  int text_end;
  long offset;
  int len;
  int ffdos = !no_ff && (get_fileformat(buf) == EOL_DOS);
  int extra = 0;

  // take care of cached line first. Only needed if the cached line is before
  // the requested line. Additionally cache the value for the cached line.
  // This is used by the extmark code which needs the byte offset of the edited
  // line. So when doing multiple small edits on the same line the value is
  // only calculated once.
  //
  // NB: caching doesn't work with 'fileformat'. This is not a problem for
  // bytetracking, as bytetracking ignores 'fileformat' option. But calling
  // line2byte() will invalidate the cache for the time being (this function
  // was never cached to start with anyway).
  bool can_cache = (lnum != 0 && !ffdos && buf->b_ml.ml_line_lnum == lnum);
  if (lnum == 0 || buf->b_ml.ml_line_lnum < lnum || !no_ff) {
    ml_flush_line(curbuf);
  } else if (can_cache && buf->b_ml.ml_line_offset > 0) {
    return buf->b_ml.ml_line_offset;
  }

  if (buf->b_ml.ml_usedchunks == -1
      || buf->b_ml.ml_chunksize == NULL
      || lnum < 0) {
    return -1;
  }

  if (offp == NULL) {
    offset = 0;
  } else {
    offset = *offp;
  }
  if (lnum == 0 && offset <= 0) {
    return 1;       // Not a "find offset" and offset 0 _must_ be in line 1
  }
  /*
   * Find the last chunk before the one containing our line. Last chunk is
   * special because it will never qualify
   */
  curline = 1;
  curix = size = 0;
  while (curix < buf->b_ml.ml_usedchunks - 1
         && ((lnum != 0
              && lnum >= curline + buf->b_ml.ml_chunksize[curix].mlcs_numlines)
             || (offset != 0
                 && offset > size +
                 buf->b_ml.ml_chunksize[curix].mlcs_totalsize
                 + ffdos * buf->b_ml.ml_chunksize[curix].mlcs_numlines))) {
    curline += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    size += buf->b_ml.ml_chunksize[curix].mlcs_totalsize;
    if (offset && ffdos) {
      size += buf->b_ml.ml_chunksize[curix].mlcs_numlines;
    }
    curix++;
  }

  while ((lnum != 0 && curline < lnum) || (offset != 0 && size < offset)) {
    if (curline > buf->b_ml.ml_line_count
        || (hp = ml_find_line(buf, curline, ML_FIND)) == NULL) {
      return -1;
    }
    dp = hp->bh_data;
    count = (long)(buf->b_ml.ml_locked_high) -
            (long)(buf->b_ml.ml_locked_low) + 1;
    start_idx = idx = curline - buf->b_ml.ml_locked_low;
    if (idx == 0) {  // first line in block, text at the end
      text_end = dp->db_txt_end;
    } else {
      text_end = ((dp->db_index[idx - 1]) & DB_INDEX_MASK);
    }
    // Compute index of last line to use in this MEMLINE
    if (lnum != 0) {
      if (curline + (count - idx) >= lnum) {
        idx += lnum - curline - 1;
      } else {
        idx = count - 1;
      }
    } else {
      extra = 0;
      while (offset >= size
             + text_end - (int)((dp->db_index[idx]) & DB_INDEX_MASK)
             + ffdos) {
        if (ffdos) {
          size++;
        }
        if (idx == count - 1) {
          extra = 1;
          break;
        }
        idx++;
      }
    }
    len = text_end - ((dp->db_index[idx]) & DB_INDEX_MASK);
    size += len;
    if (offset != 0 && size >= offset) {
      if (size + ffdos == offset) {
        *offp = 0;
      } else if (idx == start_idx) {
        *offp = offset - size + len;
      } else {
        *offp = offset - size + len
                - (text_end - ((dp->db_index[idx - 1]) & DB_INDEX_MASK));
      }
      curline += idx - start_idx + extra;
      if (curline > buf->b_ml.ml_line_count) {
        return -1;              // exactly one byte beyond the end
      }
      return curline;
    }
    curline = buf->b_ml.ml_locked_high + 1;
  }

  if (lnum != 0) {
    // Count extra CR characters.
    if (ffdos) {
      size += lnum - 1;
    }

    // Don't count the last line break if 'noeol' and ('bin' or
    // 'nofixeol').
    if ((!buf->b_p_fixeol || buf->b_p_bin) && !buf->b_p_eol
        && lnum > buf->b_ml.ml_line_count) {
      size -= ffdos + 1;
    }
  }

  if (can_cache && size > 0) {
    buf->b_ml.ml_line_offset = size;
  }

  return size;
}

/// Goto byte in buffer with offset 'cnt'.
void goto_byte(long cnt)
{
  long boff = cnt;
  linenr_T lnum;

  ml_flush_line(curbuf);  // cached line may be dirty
  setpcmark();
  if (boff) {
    boff--;
  }
  lnum = ml_find_line_or_offset(curbuf, (linenr_T)0, &boff, false);
  if (lnum < 1) {         // past the end
    curwin->w_cursor.lnum = curbuf->b_ml.ml_line_count;
    curwin->w_curswant = MAXCOL;
    coladvance(MAXCOL);
  } else {
    curwin->w_cursor.lnum = lnum;
    curwin->w_cursor.col = (colnr_T)boff;
    curwin->w_cursor.coladd = 0;
    curwin->w_set_curswant = TRUE;
  }
  check_cursor();

  // Make sure the cursor is on the first byte of a multi-byte char.
  mb_adjust_cursor();
}

/// Increment the line pointer "lp" crossing line boundaries as necessary.
/// Return 1 when going to the next line.
/// Return 2 when moving forward onto a NUL at the end of the line).
/// Return -1 when at the end of file.
/// Return 0 otherwise.
int inc(pos_T *lp)
{
  // when searching position may be set to end of a line
  if (lp->col != MAXCOL) {
    const char_u *const p = ml_get_pos(lp);
    if (*p != NUL) {  // still within line, move to next char (may be NUL)
      const int l = utfc_ptr2len(p);

      lp->col += l;
      return ((p[l] != NUL) ? 0 : 2);
    }
  }
  if (lp->lnum != curbuf->b_ml.ml_line_count) {     // there is a next line
    lp->col = 0;
    lp->lnum++;
    lp->coladd = 0;
    return 1;
  }
  return -1;
}

/// Same as inc(), but skip NUL at the end of non-empty lines.
int incl(pos_T *lp)
{
  int r;

  if ((r = inc(lp)) >= 1 && lp->col) {
    r = inc(lp);
  }
  return r;
}

int dec(pos_T *lp)
{
  lp->coladd = 0;
  if (lp->col == MAXCOL) {
    // past end of line
    char_u *p = ml_get(lp->lnum);
    lp->col = (colnr_T)STRLEN(p);
    lp->col -= utf_head_off(p, p + lp->col);
    return 0;
  }

  if (lp->col > 0) {
    // still within line
    lp->col--;
    char_u *p = ml_get(lp->lnum);
    lp->col -= utf_head_off(p, p + lp->col);
    return 0;
  }
  if (lp->lnum > 1) {
    // there is a prior line
    lp->lnum--;
    char_u *p = ml_get(lp->lnum);
    lp->col = (colnr_T)STRLEN(p);
    lp->col -= utf_head_off(p, p + lp->col);
    return 1;
  }

  // at start of file
  return -1;
}

/// Same as dec(), but skip NUL at the end of non-empty lines.
int decl(pos_T *lp)
{
  int r;

  if ((r = dec(lp)) == 1 && lp->col) {
    r = dec(lp);
  }
  return r;
}