sysdeps/generic/strcasestr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994, 1996, 1997 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 Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    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    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 /*
  21  * My personal strstr() implementation that beats most other algorithms.
  22  * Until someone tells me otherwise, I assume that this is the
  23  * fastest implementation of strstr() in C.
  24  * I deliberately chose not to comment it.  You should have at least
  25  * as much fun trying to understand it, as I had to write it :-).
  26  *
  27  * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
  28
  29 #if HAVE_CONFIG_H
  30 # include <config.h>
  31 #endif
  32
  33 #include <ctype.h>
  34
  35 #if defined _LIBC || defined HAVE_STRING_H
  36 # include <string.h>
  37 #endif
  38
  39 typedef unsigned chartype;
  40
  41 #undef strstr
  42
  43 char *
  44 __strcasestr (phaystack, pneedle)
  45      const char *phaystack;
  46      const char *pneedle;
  47 {
  48   register const unsigned char *haystack, *needle;
  49   register chartype b, c;
  50
  51   haystack = (const unsigned char *) phaystack;
  52   needle = (const unsigned char *) pneedle;
  53
  54   b = tolower (*needle);
  55   if (b != '\0')
  56     {
  57       haystack--;                               /* possible ANSI violation */
  58       do
  59         {
  60           c = *++haystack;
  61           if (c == '\0')
  62             goto ret0;
  63         }
  64       while (tolower (c) != b);
  65
  66       c = tolower (*++needle);
  67       if (c == '\0')
  68         goto foundneedle;
  69       ++needle;
  70       goto jin;
  71
  72       for (;;)
  73         {
  74           register chartype a;
  75           register const unsigned char *rhaystack, *rneedle;
  76
  77           do
  78             {
  79               a = *++haystack;
  80               if (a == '\0')
  81                 goto ret0;
  82               if (tolower (a) == b)
  83                 break;
  84               a = *++haystack;
  85               if (a == '\0')
  86                 goto ret0;
  87 shloop:     }
  88           while (tolower (a) != b);
  89
  90 jin:      a = *++haystack;
  91           if (a == '\0')
  92             goto ret0;
  93
  94           if (tolower (a) != c)
  95             goto shloop;
  96
  97           rhaystack = haystack-- + 1;
  98           rneedle = needle;
  99           a = tolower (*rneedle);
 100
 101           if (tolower (*rhaystack) == a)
 102             do
 103               {
 104                 if (a == '\0')
 105                   goto foundneedle;
 106                 ++rhaystack;
 107                 a = tolower (*++needle);
 108                 if (tolower (*rhaystack) != a)
 109                   break;
 110                 if (a == '\0')
 111                   goto foundneedle;
 112                 ++rhaystack;
 113                 a = tolower (*++needle);
 114               }
 115             while (tolower (*rhaystack) == a);
 116
 117           needle = rneedle;             /* took the register-poor approach */
 118
 119           if (a == '\0')
 120             break;
 121         }
 122     }
 123 foundneedle:
 124   return (char*) haystack;
 125 ret0:
 126   return 0;
 127 }
 128
 129 weak_alias (__strcasestr, strcasestr)