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Re: c-strstr: add testcase

From: Bruno Haible
Subject: Re: c-strstr: add testcase
Date: Sun, 11 Feb 2007 15:03:45 +0100
User-agent: KMail/1.5.4

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  <address@hidden>

        * 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 <address@hidden>, 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
   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;

      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.  */
    return (char *) haystack;

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