strcasestr.c
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	/* strcasestr.c -- case insensitive substring search in C locale
	Copyright (C) 2005 Free Software Foundation, Inc.
	Written by Bruno Haible <bruno@clisp.org>, 2005.

	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 "defines.h"

	/* Find the first occurrence of NEEDLE in HAYSTACK, using case-insensitive
	comparison.
	Note: This function may, in multibyte locales, return success even if
	strlen (haystack) < strlen (needle) ! */
	char *
	rpl_strcasestr (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 = tolower ((unsigned char) *needle);

	needle++;
	for (;; haystack++)
	{
	if (*haystack == '\0')
	/* No match. */
	return NULL;
	if (tolower ((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 (tolower ((unsigned char) *rhaystack)
	!= tolower ((unsigned char) *rneedle))
	/* Nothing in this round. */
	break;
	}
	}
	}
	}
	else
	return (char *) haystack;
	}

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