File: amemxfrm.c

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/* Locale dependent memory area transformation for comparison.
   Copyright (C) 2009-2018 Free Software Foundation, Inc.
   Written by Bruno Haible <bruno@clisp.org>, 2009.

   This program is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at your
       option) any later version.

   or both in parallel, as here.
   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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include "amemxfrm.h"

#include <errno.h>
#include <stdlib.h>
#include <string.h>

char *
amemxfrm (char *s, size_t n, char *resultbuf, size_t *lengthp)
{
  /* Result accumulator.  */
  char *result;
  size_t length;
  size_t allocated;

  char orig_sentinel;

  /* Initial memory allocation.  */
  if (resultbuf != NULL && *lengthp > 0)
    {
      result = resultbuf;
      allocated = *lengthp;
    }
  else
    {
      allocated = (n > 0 ? n : 1);
      result = (char *) malloc (allocated);
      if (result == NULL)
        goto out_of_memory_2;
    }
  length = 0;

  /* Add sentinel.byte.  */
  orig_sentinel = s[n];
  s[n] = '\0';

  /* Iterate through S, transforming each NUL terminated segment.
     Accumulate the resulting transformed segments in result, separated by
     NULs.  */
  {
    const char *p_end = s + n + 1;
    const char *p;

    p = s;
    for (;;)
      {
        /* Search next NUL byte.  */
        size_t l = strlen (p);

        for (;;)
          {
            size_t k;

            /* A call to strxfrm costs about 20 times more than a call to
               strdup of the result.  Therefore it is worth to try to avoid
               calling strxfrm more than once on a given string, by making
               enough room before calling strxfrm.
               The size of the strxfrm result, k, is likely to be between
               l and 3 * l.  */
            if (3 * l >= allocated - length)
              {
                /* Grow the result buffer.  */
                size_t new_allocated;
                char *new_result;

                new_allocated = length + 3 * l + 1;
                if (new_allocated < 2 * allocated)
                  new_allocated = 2 * allocated;
                if (new_allocated < 64)
                  new_allocated = 64;
                if (result == resultbuf)
                  new_result = (char *) malloc (new_allocated);
                else
                  new_result = (char *) realloc (result, new_allocated);
                if (new_result != NULL)
                  {
                    allocated = new_allocated;
                    result = new_result;
                  }
              }

            errno = 0;
            k = strxfrm (result + length, p, allocated - length);
            if (errno != 0)
              goto fail;
            if (k >= allocated - length)
              {
                /* Grow the result buffer.  */
                size_t new_allocated;
                char *new_result;

                new_allocated = length + k + 1;
                if (new_allocated < 2 * allocated)
                  new_allocated = 2 * allocated;
                if (new_allocated < 64)
                  new_allocated = 64;
                if (result == resultbuf)
                  new_result = (char *) malloc (new_allocated);
                else
                  new_result = (char *) realloc (result, new_allocated);
                if (new_result == NULL)
                  goto out_of_memory_1;
                allocated = new_allocated;
                result = new_result;
              }
            else
              {
                length += k;
                break;
              }
          }

        p = p + l + 1;
        if (p == p_end)
          break;
        result[length] = '\0';
        length++;
      }
  }

  /* Shrink the allocated memory if possible.
     It is not worth calling realloc when length + 1 == allocated; it would
     save just one byte.  */
  if (result != resultbuf && length + 1 < allocated)
    {
      if ((length > 0 ? length : 1) <= *lengthp)
        {
          memcpy (resultbuf, result, length);
          free (result);
          result = resultbuf;
        }
      else
        {
          char *memory = (char *) realloc (result, length > 0 ? length : 1);
          if (memory != NULL)
            result = memory;
        }
    }

  s[n] = orig_sentinel;
  *lengthp = length;
  return result;

 fail:
  {
    int saved_errno = errno;
    if (result != resultbuf)
      free (result);
    s[n] = orig_sentinel;
    errno = saved_errno;
    return NULL;
  }

 out_of_memory_1:
  if (result != resultbuf)
    free (result);
  s[n] = orig_sentinel;
 out_of_memory_2:
  errno = ENOMEM;
  return NULL;
}