Rewrite c-strstr.c for maintainability.

diff --git a/ChangeLog b/ChangeLog
index 79fe34200730831d07f49df8b12b345fbc436de5..1e5cda365526b2f1da226a61d04591efce7dedb9 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2007-02-11  Bruno Haible  <bruno@clisp.org>
 
+       * lib/c-strstr.c: Complete rewrite for maintainability.
+
        * modules/c-strstr-tests: New file.
        * tests/test-c-strstr.c: New file.
 

diff --git a/lib/c-strstr.c b/lib/c-strstr.c
index b015a6336e1acd2d1528bb863bb38e6fc3931215..a3623f650a45ff00d1535b360c3c36727410f32e 100644 (file)
--- a/lib/c-strstr.c
+++ b/lib/c-strstr.c
@@ -1,118 +1,70 @@
-/* Copyright (C) 1994, 1999, 2002-2003, 2005-2006 Free Software Foundation, Inc.
-This file is part of the GNU C Library.
+/* c-strstr.c -- substring search in C locale
+   Copyright (C) 2005-2007 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2005, 2007.
 
-This program is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
-any later version.
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
 
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
 
-You should have received a copy of the GNU General Public License
-along with this program; if not, write to the Free Software Foundation,
-Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
-
-/*
- * My personal strstr() implementation that beats most other algorithms.
- * Until someone tells me otherwise, I assume that this is the
- * fastest implementation of strstr() in C.
- * I deliberately chose not to comment it.  You should have at least
- * as much fun trying to understand it, as I had to write it :-).
- *
- * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de        */
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
 #include <config.h>
 
 /* Specification.  */
 #include "c-strstr.h"
 
-#include <string.h>
-
-typedef unsigned chartype;
+#include <stddef.h>
 
+/* Find the first occurrence of NEEDLE in HAYSTACK.  */
 char *
-c_strstr (const char *phaystack, const char *pneedle)
+c_strstr (const char *haystack, const char *needle)
 {
-  register const unsigned char *haystack, *needle;
-  register chartype b, c;
-
-  haystack = (const unsigned char *) phaystack;
-  needle = (const unsigned char *) pneedle;
-
-  b = *needle;
-  if (b != '\0')
+  /* Be careful not to look at the entire extent of haystack or needle
+     until needed.  This is useful because of these two cases:
+       - haystack may be very long, and a match of needle found early,
+       - needle may be very long, and not even a short initial segment of
+         needle may be found in haystack.  */
+  if (*needle != '\0')
     {
-      haystack--;                              /* possible ANSI violation */
-      do
-       {
-         c = *++haystack;
-         if (c == '\0')
-           goto ret0;
-       }
-      while (c != b);
-
-      c = *++needle;
-      if (c == '\0')
-       goto foundneedle;
-      ++needle;
-      goto jin;
-
-      for (;;)
-        {
-          register chartype a;
-         register const unsigned char *rhaystack, *rneedle;
+      /* Speed up the following searches of needle by caching its first
+        character.  */
+      unsigned char b = (unsigned char) *needle;
 
-         do
+      needle++;
+      for (;; haystack++)
+       {
+         if (*haystack == '\0')
+           /* No match.  */
+           return NULL;
+         if ((unsigned char) *haystack == b)
+           /* The first character matches.  */
            {
-             a = *++haystack;
-             if (a == '\0')
-               goto ret0;
-             if (a == b)
-               break;
-             a = *++haystack;
-             if (a == '\0')
-               goto ret0;
-shloop:;    }
-          while (a != b);
-
-jin:     a = *++haystack;
-         if (a == '\0')
-           goto ret0;
-
-         if (a != c)
-           goto shloop;
-
-         rhaystack = haystack-- + 1;
-         rneedle = needle;
-         a = *rneedle;
-
-         if (*rhaystack == a)
-           do
-             {
-               if (a == '\0')
-                 goto foundneedle;
-               ++rhaystack;
-               a = *++needle;
-               if (*rhaystack != a)
-                 break;
-               if (a == '\0')
-                 goto foundneedle;
-               ++rhaystack;
-               a = *++needle;
-             }
-           while (*rhaystack == a);
-
-         needle = rneedle;                /* took the register-poor approach */
-
-         if (a == '\0')
-           break;
-        }
+             const char *rhaystack = haystack + 1;
+             const char *rneedle = needle;
+
+             for (;; rhaystack++, rneedle++)
+               {
+                 if (*rneedle == '\0')
+                   /* Found a match.  */
+                   return (char *) haystack;
+                 if (*rhaystack == '\0')
+                   /* No match.  */
+                   return NULL;
+                 if ((unsigned char) *rhaystack != (unsigned char) *rneedle)
+                   /* Nothing in this round.  */
+                   break;
+               }
+           }
+       }
     }
-foundneedle:
-  return (char *) haystack;
-ret0:
-  return 0;
+  else
+    return (char *) haystack;
 }