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  1. /* Copyright (C) 1991,92,93,94,96,97,98,2000,2004,2007,2011 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. }
  72.