/* Copyright (C) 1991-2024 Free Software Foundation, Inc.
  This file is part of the GNU C Library.

  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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/*

@deftypefn Supplemental void* memmem (const void *@var{haystack}, @
 size_t @var{haystack_len} const void *@var{needle}, size_t @var{needle_len})

Returns a pointer to the first occurrence of @var{needle} (length
@var{needle_len}) in @var{haystack} (length @var{haystack_len}).
Returns @code{NULL} if not found.

@end deftypefn

*/

#ifndef _LIBC
# include <config.h>
#endif

#include <stddef.h>
#include <string.h>

#ifndef _LIBC
# define __builtin_expect(expr, val)   (expr)
#endif

#undef memmem

/* Return the first occurrence of NEEDLE in HAYSTACK.  */
void *
memmem (const void *haystack, size_t haystack_len, const void *needle,
       size_t needle_len)
{
 const char *begin;
 const char *const last_possible
   = (const char *) haystack + haystack_len - needle_len;

 if (needle_len == 0)
   /* The first occurrence of the empty string is deemed to occur at
      the beginning of the string.  */
   return (void *) haystack;

 /* Sanity check, otherwise the loop might search through the whole
    memory.  */
 if (__builtin_expect (haystack_len < needle_len, 0))
   return NULL;

 for (begin = (const char *) haystack; begin <= last_possible; ++begin)
   if (begin[0] == ((const char *) needle)[0] &&
       !memcmp ((const void *) &begin[1],
                (const void *) ((const char *) needle + 1),
                needle_len - 1))
     return (void *) begin;

 return NULL;
}