string/strstr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /* This particular implementation was written by Eric Blake, 2008.  */
  20
  21 #ifndef _LIBC
  22 # include <config.h>
  23 #endif
  24
  25 /* Specification of strstr.  */
  26 #include <string.h>
  27
  28 #include <stdbool.h>
  29
  30 #ifndef _LIBC
  31 # define __builtin_expect(expr, val)   (expr)
  32 #endif
  33
  34 #define RETURN_TYPE char *
  35 #define AVAILABLE(h, h_l, j, n_l)                       \
  36   (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
  37    && ((h_l) = (j) + (n_l)))
  38 #define CHECK_EOL (1)
  39 #define RET0_IF_0(a) if (!a) goto ret0
  40 #include "str-two-way.h"
  41
  42 #undef strstr
  43
  44 #ifndef STRSTR
  45 #define STRSTR strstr
  46 #endif
  47
  48 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
  49    if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
  50    HAYSTACK.  */
  51 char *
  52 STRSTR (const char *haystack_start, const char *needle_start)
  53 {
  54   const char *haystack = haystack_start;
  55   const char *needle = needle_start;
  56   size_t needle_len; /* Length of NEEDLE.  */
  57   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  58   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  59
  60   /* Determine length of NEEDLE, and in the process, make sure
  61      HAYSTACK is at least as long (no point processing all of a long
  62      NEEDLE if HAYSTACK is too short).  */
  63   while (*haystack && *needle)
  64     ok &= *haystack++ == *needle++;
  65   if (*needle)
  66     return NULL;
  67   if (ok)
  68     return (char *) haystack_start;
  69
  70   /* Reduce the size of haystack using strchr, since it has a smaller
  71      linear coefficient than the Two-Way algorithm.  */
  72   needle_len = needle - needle_start;
  73   haystack = strchr (haystack_start + 1, *needle_start);
  74   if (!haystack || __builtin_expect (needle_len == 1, 0))
  75     return (char *) haystack;
  76   needle -= needle_len;
  77   haystack_len = (haystack > haystack_start + needle_len ? 1
  78                   : needle_len + haystack_start - haystack);
  79
  80   /* Perform the search.  Abstract memory is considered to be an array
  81      of 'unsigned char' values, not an array of 'char' values.  See
  82      ISO C 99 section 6.2.6.1.  */
  83   if (needle_len < LONG_NEEDLE_THRESHOLD)
  84     return two_way_short_needle ((const unsigned char *) haystack,
  85                                  haystack_len,
  86                                  (const unsigned char *) needle, needle_len);
  87   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  88                               (const unsigned char *) needle, needle_len);
  89 }
  90 libc_hidden_builtin_def (strstr)
  91
  92 #undef LONG_NEEDLE_THRESHOLD