mes/lib/string/memmem.c

/* -*-comment-start: "//";comment-end:""-*-
 * GNU Mes --- Maxwell Equations of Software
 * Copyright © 1997--2015,2017,2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 * Copyright (C) 1997--2015,2018 Han-Wen Nienhuys <hanwen@xs4all.nl>
 *
 * This file is part of GNU Mes.
 *
 * GNU Mes 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 3 of the License, or (at
 * your option) any later version.
 *
 * GNU Mes 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 GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <string.h>

/** locate a substring. #memmem# finds the first occurrence of
    #needle# in #haystack#.  This is not ANSI-C.

    The prototype is not in accordance with the Linux Programmer's
    Manual v1.15, but it is with /usr/include/string.h   */

unsigned char *
_memmem (unsigned char const *haystack, int haystack_len,
         unsigned char const *needle, int needle_len)
{
  unsigned char const *end_haystack = haystack + haystack_len - needle_len + 1;
  unsigned char const *end_needle = needle + needle_len;

  /* Ahhh ... Some minimal lowlevel stuff. This *is* nice; Varation
     is the spice of life */
  while (haystack < end_haystack)
    {
      unsigned char const *subneedle = needle;
      unsigned char const *subhaystack = haystack;
      while (subneedle < end_needle)
        if (*subneedle++ != *subhaystack++)
          goto next;

      /* Completed the needle.  Gotcha.  */
      return (unsigned char *) haystack;
    next:
      haystack++;
    }
  return 0;
}

void *
memmem (void const *haystack, int haystack_len,
        void const *needle, int needle_len)
{
  unsigned char const *haystack_byte_c = (unsigned char const *)haystack;
  unsigned char const *needle_byte_c = (unsigned char const *)needle;
  return _memmem (haystack_byte_c, haystack_len, needle_byte_c, needle_len);
}