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strstr.c revision 1.1.1.1 
      1 /* Searching in a string.
      2    Copyright (C) 2005-2006 Free Software Foundation, Inc.
      3    Written by Bruno Haible <bruno (at) clisp.org>, 2005.
      4 
      5    This program is free software; you can redistribute it and/or modify
      6    it under the terms of the GNU General Public License as published by
      7    the Free Software Foundation; either version 2, or (at your option)
      8    any later version.
      9 
     10    This program 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 General Public License for more details.
     14 
     15    You should have received a copy of the GNU General Public License
     16    along with this program; if not, write to the Free Software Foundation,
     17    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
     18 
     19 #include <config.h>
     20 
     21 /* Specification.  */
     22 #include "strstr.h"
     23 
     24 #include <stddef.h>  /* for NULL */
     25 
     26 #if HAVE_MBRTOWC
     27 # include "mbuiter.h"
     28 #endif
     29 
     30 /* Find the first occurrence of NEEDLE in HAYSTACK.  */
     31 char *
     32 strstr (const char *haystack, const char *needle)
     33 {
     34   /* Be careful not to look at the entire extent of haystack or needle
     35      until needed.  This is useful because of these two cases:
     36        - haystack may be very long, and a match of needle found early,
     37        - needle may be very long, and not even a short initial segment of
     38          needle may be found in haystack.  */
     39 #if HAVE_MBRTOWC
     40   if (MB_CUR_MAX > 1)
     41     {
     42       mbui_iterator_t iter_needle;
     43 
     44       mbui_init (iter_needle, needle);
     45       if (mbui_avail (iter_needle))
     46 	{
     47 	  mbui_iterator_t iter_haystack;
     48 
     49 	  mbui_init (iter_haystack, haystack);
     50 	  for (;; mbui_advance (iter_haystack))
     51 	    {
     52 	      if (!mbui_avail (iter_haystack))
     53 		/* No match.  */
     54 		return NULL;
     55 
     56 	      if (mb_equal (mbui_cur (iter_haystack), mbui_cur (iter_needle)))
     57 		/* The first character matches.  */
     58 		{
     59 		  mbui_iterator_t rhaystack;
     60 		  mbui_iterator_t rneedle;
     61 
     62 		  memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));
     63 		  mbui_advance (rhaystack);
     64 
     65 		  mbui_init (rneedle, needle);
     66 		  if (!mbui_avail (rneedle))
     67 		    abort ();
     68 		  mbui_advance (rneedle);
     69 
     70 		  for (;; mbui_advance (rhaystack), mbui_advance (rneedle))
     71 		    {
     72 		      if (!mbui_avail (rneedle))
     73 			/* Found a match.  */
     74 			return (char *) mbui_cur_ptr (iter_haystack);
     75 		      if (!mbui_avail (rhaystack))
     76 			/* No match.  */
     77 			return NULL;
     78 		      if (!mb_equal (mbui_cur (rhaystack), mbui_cur (rneedle)))
     79 			/* Nothing in this round.  */
     80 			break;
     81 		    }
     82 		}
     83 	    }
     84 	}
     85       else
     86 	return (char *) haystack;
     87     }
     88   else
     89 #endif
     90     {
     91       if (*needle != '\0')
     92 	{
     93 	  /* Speed up the following searches of needle by caching its first
     94 	     character.  */
     95 	  char b = *needle++;
     96 
     97 	  for (;; haystack++)
     98 	    {
     99 	      if (*haystack == '\0')
    100 		/* No match.  */
    101 		return NULL;
    102 	      if (*haystack == b)
    103 		/* The first character matches.  */
    104 		{
    105 		  const char *rhaystack = haystack + 1;
    106 		  const char *rneedle = needle;
    107 
    108 		  for (;; rhaystack++, rneedle++)
    109 		    {
    110 		      if (*rneedle == '\0')
    111 			/* Found a match.  */
    112 			return (char *) haystack;
    113 		      if (*rhaystack == '\0')
    114 			/* No match.  */
    115 			return NULL;
    116 		      if (*rhaystack != *rneedle)
    117 			/* Nothing in this round.  */
    118 			break;
    119 		    }
    120 		}
    121 	    }
    122 	}
    123       else
    124 	return (char *) haystack;
    125     }
    126 }
    127