1  /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     This program is free software; you can redistribute it and/or modify
       5     it under the terms of the GNU General Public License as published by
       6     the Free Software Foundation; either version 2, or (at your option)
       7     any later version.
       8  
       9     This program is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU General Public License for more details.
      13  
      14     You should have received a copy of the GNU General Public License along
      15     with this program; if not, write to the Free Software Foundation,
      16     Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
      17  
      18  /*
      19  
      20  @deftypefn Supplemental void* memmem (const void *@var{haystack}, @
      21    size_t @var{haystack_len} const void *@var{needle}, size_t @var{needle_len})
      22  
      23  Returns a pointer to the first occurrence of @var{needle} (length
      24  @var{needle_len}) in @var{haystack} (length @var{haystack_len}).
      25  Returns @code{NULL} if not found.
      26  
      27  @end deftypefn
      28  
      29  */
      30  
      31  #ifndef _LIBC
      32  # include <config.h>
      33  #endif
      34  
      35  #include <stddef.h>
      36  #include <string.h>
      37  
      38  #ifndef _LIBC
      39  # define __builtin_expect(expr, val)   (expr)
      40  #endif
      41  
      42  #undef memmem
      43  
      44  /* Return the first occurrence of NEEDLE in HAYSTACK.  */
      45  void *
      46  memmem (const void *haystack, size_t haystack_len, const void *needle,
      47  	size_t needle_len)
      48  {
      49    const char *begin;
      50    const char *const last_possible
      51      = (const char *) haystack + haystack_len - needle_len;
      52  
      53    if (needle_len == 0)
      54      /* The first occurrence of the empty string is deemed to occur at
      55         the beginning of the string.  */
      56      return (void *) haystack;
      57  
      58    /* Sanity check, otherwise the loop might search through the whole
      59       memory.  */
      60    if (__builtin_expect (haystack_len < needle_len, 0))
      61      return NULL;
      62  
      63    for (begin = (const char *) haystack; begin <= last_possible; ++begin)
      64      if (begin[0] == ((const char *) needle)[0] &&
      65  	!memcmp ((const void *) &begin[1],
      66  		 (const void *) ((const char *) needle + 1),
      67  		 needle_len - 1))
      68        return (void *) begin;
      69  
      70    return NULL;
      71  }