string/strstr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994-2018 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   (((j) + (n_l) <= (h_l)) \
  37    || ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_l) + 512), \
  38        (j) + (n_l) <= (h_l)))
  39 #define CHECK_EOL (1)
  40 #define RET0_IF_0(a) if (!a) goto ret0
  41 #define FASTSEARCH(S,C,N) (void*) strchr ((void*)(S), (C))
  42 #include "str-two-way.h"
  43
  44 #undef strstr
  45
  46 #ifndef STRSTR
  47 #define STRSTR strstr
  48 #endif
  49
  50 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
  51    if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
  52    HAYSTACK.  */
  53 char *
  54 STRSTR (const char *haystack, const char *needle)
  55 {
  56   size_t needle_len; /* Length of NEEDLE.  */
  57   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  58
  59   /* Handle empty NEEDLE special case.  */
  60   if (needle[0] == '\0')
  61     return (char *) haystack;
  62
  63   /* Skip until we find the first matching char from NEEDLE.  */
  64   haystack = strchr (haystack, needle[0]);
  65   if (haystack == NULL || needle[1] == '\0')
  66     return (char *) haystack;
  67
  68   /* Ensure HAYSTACK length is at least as long as NEEDLE length.
  69      Since a match may occur early on in a huge HAYSTACK, use strnlen
  70      and read ahead a few cachelines for improved performance.  */
  71   needle_len = strlen (needle);
  72   haystack_len = __strnlen (haystack, needle_len + 256);
  73   if (haystack_len < needle_len)
  74     return NULL;
  75
  76   /* Check whether we have a match.  This improves performance since we avoid
  77      the initialization overhead of the two-way algorithm.  */
  78   if (memcmp (haystack, needle, needle_len) == 0)
  79     return (char *) haystack;
  80
  81   /* Perform the search.  Abstract memory is considered to be an array
  82      of 'unsigned char' values, not an array of 'char' values.  See
  83      ISO C 99 section 6.2.6.1.  */
  84   if (needle_len < LONG_NEEDLE_THRESHOLD)
  85     return two_way_short_needle ((const unsigned char *) haystack,
  86                                  haystack_len,
  87                                  (const unsigned char *) needle, needle_len);
  88   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  89                               (const unsigned char *) needle, needle_len);
  90 }
  91 libc_hidden_builtin_def (strstr)
  92
  93 #undef LONG_NEEDLE_THRESHOLD