The "check that the asymptotic worst-case complexity is not quadratic"
fails: it takes eternities. I'm therefore going to add a catch for
worst-case linear complexity. This is impossible with the current over-
optimized 'goto' spaghetti implementation, so I'm replacing it with a
maintainable implementation first.
2007-02-11 Bruno Haible <[EMAIL PROTECTED]>
* lib/c-strstr.c: Complete rewrite for maintainability.
============================ lib/c-strstr.c ================================
/* c-strstr.c -- substring search in C locale
Copyright (C) 2005-2007 Free Software Foundation, Inc.
Written by Bruno Haible <[EMAIL PROTECTED]>, 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 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. */
#include <config.h>
/* Specification. */
#include "c-strstr.h"
#include <stddef.h>
/* Find the first occurrence of NEEDLE in HAYSTACK. */
char *
c_strstr (const char *haystack, const char *needle)
{
/* 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')
{
/* Speed up the following searches of needle by caching its first
character. */
unsigned char b = (unsigned char) *needle;
needle++;
for (;; haystack++)
{
if (*haystack == '\0')
/* No match. */
return NULL;
if ((unsigned char) *haystack == b)
/* The first character matches. */
{
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;
}
}
}
}
else
return (char *) haystack;
}
