ffs.s

基于组件方式开发操作系统的OSKIT源代码

/*
 * Copyright (c) 1993 Winning Strategies, Inc.
 * All rights reserved.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Winning Strategies, Inc.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software withough specific prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 *
 *	$Id: ffs.S,v 1.4 1997/02/22 14:59:05 peter Exp $
 */

#if defined(LIBC_RCS) && !defined(lint)
	.text
        .asciz "$Id: ffs.S,v 1.4 1997/02/22 14:59:05 peter Exp $"
#endif /* LIBC_RCS and not lint */

#include "DEFS.h"

/*
 * ffs(value)
 *	finds the first bit set in value and returns the index of 
 *	that bit.  Bits are numbered starting from 1, starting at the
 *	rightmost bit.  A return value of 0 means that the argument
 *	was zero.
 *
 * Written by:
 *	J.T. Conklin ([e-mail]), Winning Strategies, Inc.
 */

ENTRY(ffs)
	bsfl	4(%esp),%eax
	jz	L1	 		/* ZF is set if all bits are 0 */
	incl	%eax			/* bits numbered from 1, not 0 */
	ret

	.align 2
L1:	xorl	%eax,%eax		/* clear result */
	ret