sysdeps/generic/strcasestr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994, 1996, 1997, 1998, 1999 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 strcasestr
  42 #undef __strcasestr
  43
  44 char *
  45 __strcasestr (phaystack, pneedle)
  46      const char *phaystack;
  47      const char *pneedle;
  48 {
  49   register const unsigned char *haystack, *needle;
  50   register chartype b, c;
  51
  52   haystack = (const unsigned char *) phaystack;
  53   needle = (const unsigned char *) pneedle;
  54
  55   b = _tolower (*needle);
  56   if (b != '\0')
  57     {
  58       haystack--;                               /* possible ANSI violation */
  59       do
  60         {
  61           c = *++haystack;
  62           if (c == '\0')
  63             goto ret0;
  64         }
  65       while (_tolower (c) != b);
  66
  67       c = _tolower (*++needle);
  68       if (c == '\0')
  69         goto foundneedle;
  70       ++needle;
  71       goto jin;
  72
  73       for (;;)
  74         {
  75           register chartype a;
  76           register const unsigned char *rhaystack, *rneedle;
  77
  78           do
  79             {
  80               a = *++haystack;
  81               if (a == '\0')
  82                 goto ret0;
  83               if (_tolower (a) == b)
  84                 break;
  85               a = *++haystack;
  86               if (a == '\0')
  87                 goto ret0;
  88 shloop:     }
  89           while (_tolower (a) != b);
  90
  91 jin:      a = *++haystack;
  92           if (a == '\0')
  93             goto ret0;
  94
  95           if (_tolower (a) != c)
  96             goto shloop;
  97
  98           rhaystack = haystack-- + 1;
  99           rneedle = needle;
 100           a = _tolower (*rneedle);
 101
 102           if (_tolower (*rhaystack) == a)
 103             do
 104               {
 105                 if (a == '\0')
 106                   goto foundneedle;
 107                 ++rhaystack;
 108                 a = _tolower (*++needle);
 109                 if (_tolower (*rhaystack) != a)
 110                   break;
 111                 if (a == '\0')
 112                   goto foundneedle;
 113                 ++rhaystack;
 114                 a = _tolower (*++needle);
 115               }
 116             while (_tolower (*rhaystack) == a);
 117
 118           needle = rneedle;             /* took the register-poor approach */
 119
 120           if (a == '\0')
 121             break;
 122         }
 123     }
 124 foundneedle:
 125   return (char*) haystack;
 126 ret0:
 127   return 0;
 128 }
 129
 130 weak_alias (__strcasestr, strcasestr)