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same.c

/* Determine whether two file names refer to the same file.
   Copyright (C) 1997-2000, 2002-2003 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* written by Jim Meyering */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdbool.h>
#include <stdio.h>
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <ctype.h>
#include <errno.h>
#ifndef errno
extern int errno;
#endif

#include <string.h>

#include <limits.h>
#ifndef _POSIX_NAME_MAX
# define _POSIX_NAME_MAX 14
#endif

#include "same.h"
#include "dirname.h"
#include "error.h"
#include "xalloc.h"

#define MIN(a, b) ((a) < (b) ? (a) : (b))

#define SAME_INODE(Stat_buf_1, Stat_buf_2) \
  ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \
   && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev)

/* Return nonzero if SOURCE and DEST point to the same name in the same
   directory.  */

int
same_name (const char *source, const char *dest)
{
  /* Compare the basenames.  */
  char const *source_basename = base_name (source);
  char const *dest_basename = base_name (dest);
  size_t source_baselen = base_len (source_basename);
  size_t dest_baselen = base_len (dest_basename);
  bool identical_basenames =
    (source_baselen == dest_baselen
     && memcmp (source_basename, dest_basename, dest_baselen) == 0);
  bool compare_dirs = identical_basenames;
  bool same = false;

#if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
  /* This implementation silently truncates pathname components.  If
     the base names might be truncated, check whether the truncated
     base names are the same, while checking the directories.  */
  size_t slen_max = HAVE_LONG_FILE_NAMES ? 255 : _POSIX_NAME_MAX;
  size_t min_baselen = MIN (source_baselen, dest_baselen);
  if (slen_max <= min_baselen
      && memcmp (source_basename, dest_basename, slen_max) == 0)
    compare_dirs = true;
#endif

  if (compare_dirs)
    {
      struct stat source_dir_stats;
      struct stat dest_dir_stats;
      char *source_dirname, *dest_dirname;

      /* Compare the parent directories (via the device and inode numbers).  */
      source_dirname = dir_name (source);
      dest_dirname = dir_name (dest);

      if (stat (source_dirname, &source_dir_stats))
      {
        /* Shouldn't happen.  */
        error (1, errno, "%s", source_dirname);
      }

      if (stat (dest_dirname, &dest_dir_stats))
      {
        /* Shouldn't happen.  */
        error (1, errno, "%s", dest_dirname);
      }

      same = SAME_INODE (source_dir_stats, dest_dir_stats);

#if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
      if (same && ! identical_basenames)
      {
        long name_max = (errno = 0, pathconf (dest_dirname, _PC_NAME_MAX));
        if (name_max < 0)
          {
            if (errno)
            {
              /* Shouldn't happen.  */
              error (1, errno, "%s", dest_dirname);
            }
            same = false;
          }
        else
          same = (name_max <= min_baselen
                && memcmp (source_basename, dest_basename, name_max) == 0);
      }
#endif

      free (source_dirname);
      free (dest_dirname);
    }

  return same;
}

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