gl/strstr.c

   1 /* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2024 Free Software
   2    Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* This particular implementation was written by Eric Blake, 2008.  */
  19
  20 #ifndef _LIBC
  21 # include <config.h>
  22 #endif
  23
  24 /* Specification of strstr.  */
  25 #include <string.h>
  26
  27 #define RETURN_TYPE char *
  28 #define AVAILABLE(h, h_l, j, n_l)                       \
  29   (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
  30    && ((h_l) = (j) + (n_l)))
  31 #include "str-two-way.h"
  32
  33 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
  34    if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
  35    HAYSTACK.  */
  36 char *
  37 strstr (const char *haystack_start, const char *needle_start)
  38 {
  39   const char *haystack = haystack_start;
  40   const char *needle = needle_start;
  41   size_t needle_len; /* Length of NEEDLE.  */
  42   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  43   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  44
  45   /* Determine length of NEEDLE, and in the process, make sure
  46      HAYSTACK is at least as long (no point processing all of a long
  47      NEEDLE if HAYSTACK is too short).  */
  48   while (*haystack && *needle)
  49     ok &= *haystack++ == *needle++;
  50   if (*needle)
  51     return NULL;
  52   if (ok)
  53     return (char *) haystack_start;
  54
  55   /* Reduce the size of haystack using strchr, since it has a smaller
  56      linear coefficient than the Two-Way algorithm.  */
  57   needle_len = needle - needle_start;
  58   haystack = strchr (haystack_start + 1, *needle_start);
  59   if (!haystack || __builtin_expect (needle_len == 1, 0))
  60     return (char *) haystack;
  61   needle -= needle_len;
  62   haystack_len = (haystack > haystack_start + needle_len ? 1
  63                   : needle_len + haystack_start - haystack);
  64
  65   /* Perform the search.  Abstract memory is considered to be an array
  66      of 'unsigned char' values, not an array of 'char' values.  See
  67      ISO C 99 section 6.2.6.1.  */
  68   if (needle_len < LONG_NEEDLE_THRESHOLD)
  69     return two_way_short_needle ((const unsigned char *) haystack,
  70                                  haystack_len,
  71                                  (const unsigned char *) needle, needle_len);
  72   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  73                               (const unsigned char *) needle, needle_len);
  74 }
  75
  76 #undef LONG_NEEDLE_THRESHOLD