Source to machdep/i386/libc/ffs.c


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/*
 * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * "Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
 * Reserved.  This file contains Original Code and/or Modifications of
 * Original Code as defined in and that are subject to the Apple Public
 * Source License Version 1.0 (the 'License').  You may not use this file
 * except in compliance with the License.  Please obtain a copy of the
 * License at http://www.apple.com/publicsource and read it before using
 * this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License."
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

/* Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved.
 *
 *      File:   machdep/i386/libc/ffs.c
 *      Author: Bruce Martin, NeXT Computer, Inc.
 *
 *      This file contains machine dependent code for the ffs function
 *      on NeXT i386-based products.  Currently tuned for the i486.
 *
 * HISTORY
 * 27-Sep-92  Bruce Martin (Bruce_Martin@NeXT.COM)
 *	Created: stolen from Mike's code.
 */

unsigned
ffs(unsigned mask)
{
	unsigned bitpos;

	if (mask == 0)
		return 0;

	bitpos = 1;
	while ((mask & 0xff) == 0) {
		bitpos += 8;
		mask >>= 8;
	}
	while ((mask & 1) == 0) {
		bitpos += 1;
		mask >>= 1;
	}
	return bitpos;
}