memmem.c 1.8 KB

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  1. /* Copyright (C) 1991,92,93,94,96,97,98,2000 Free Software Foundation, Inc.
  2. This file is part of the GNU C Library.
  3. The GNU C Library is free software; you can redistribute it and/or
  4. modify it under the terms of the GNU Lesser General Public
  5. License as published by the Free Software Foundation; either
  6. version 2.1 of the License, or (at your option) any later version.
  7. The GNU C Library is distributed in the hope that it will be useful,
  8. but WITHOUT ANY WARRANTY; without even the implied warranty of
  9. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  10. Lesser General Public License for more details.
  11. You should have received a copy of the GNU Lesser General Public
  12. License along with the GNU C Library; if not, write to the Free
  13. Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  14. 02111-1307 USA. */
  15. #include <string.h>
  16. #include <stddef.h>
  17. #undef memmem
  18. /* Return the first occurrence of NEEDLE in HAYSTACK. */
  19. void *memmem (const void *haystack, size_t haystack_len,
  20. const void *needle, size_t needle_len)
  21. {
  22. const char *begin;
  23. const char *const last_possible
  24. = (const char *) haystack + haystack_len - needle_len;
  25. if (needle_len == 0)
  26. /* The first occurrence of the empty string is deemed to occur at
  27. the beginning of the string. */
  28. return (void *) haystack;
  29. /* Sanity check, otherwise the loop might search through the whole
  30. memory. */
  31. if (__builtin_expect (haystack_len < needle_len, 0))
  32. return NULL;
  33. for (begin = (const char *) haystack; begin <= last_possible; ++begin)
  34. if (begin[0] == ((const char *) needle)[0] &&
  35. !memcmp ((const void *) &begin[1],
  36. (const void *) ((const char *) needle + 1),
  37. needle_len - 1))
  38. return (void *) begin;
  39. return NULL;
  40. }