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guard single-dot from modification by the application
(SUSv3 spec don't forbid this brutal operation).
this idea taken from OpenBSD's version of basename(3) and dirname(3).

/*	$NetBSD: dirname.c,v 1.11 2009/11/24 13:34:20 tnozaki Exp $	*/

/*-
 * Copyright (c) 1997, 2002 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Klaus Klein and Jason R. Thorpe.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: dirname.c,v 1.11 2009/11/24 13:34:20 tnozaki Exp $");
#endif /* !LIBC_SCCS && !lint */

#include "namespace.h"
#include <libgen.h>
#include <limits.h>
#include <string.h>

#ifdef __weak_alias
__weak_alias(dirname,_dirname)
#endif

#if !HAVE_DIRNAME
char *
dirname(char *path)
{
	static char result[PATH_MAX];
	const char *lastp;
	size_t len;

	/*
	 * If `path' is a null pointer or points to an empty string,
	 * return a pointer to the string ".".
	 */
	if ((path == NULL) || (*path == '\0'))
		goto singledot;


	/* Strip trailing slashes, if any. */
	lastp = path + strlen(path) - 1;
	while (lastp != path && *lastp == '/')
		lastp--;

	/* Terminate path at the last occurence of '/'. */
	do {
		if (*lastp == '/') {
			/* Strip trailing slashes, if any. */
			while (lastp != path && *lastp == '/')
				lastp--;

			/* ...and copy the result into the result buffer. */
			len = (lastp - path) + 1 /* last char */;
			if (len > (PATH_MAX - 1))
				len = PATH_MAX - 1;

			memcpy(result, path, len);
			result[len] = '\0';

			return (result);
		}
	} while (--lastp >= path);

	/* No /'s found, return a pointer to the string ".". */
singledot:
	result[0] = '.';
	result[1] = '\0';

	return (result);
}
#endif