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Annotation of kernel/machdep/ppc/libc/ffs.s, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
        !             3:  *
        !             4:  * @APPLE_LICENSE_HEADER_START@
        !             5:  * 
        !             6:  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
        !             7:  * Reserved.  This file contains Original Code and/or Modifications of
        !             8:  * Original Code as defined in and that are subject to the Apple Public
        !             9:  * Source License Version 1.1 (the "License").  You may not use this file
        !            10:  * except in compliance with the License.  Please obtain a copy of the
        !            11:  * License at http://www.apple.com/publicsource and read it before using
        !            12:  * this file.
        !            13:  * 
        !            14:  * The Original Code and all software distributed under the License are
        !            15:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
        !            16:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
        !            17:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
        !            18:  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
        !            19:  * License for the specific language governing rights and limitations
        !            20:  * under the License.
        !            21:  * 
        !            22:  * @APPLE_LICENSE_HEADER_END@
        !            23:  */
        !            24: 
        !            25: /* Copyright (c) 1992, 1997-1998 Apple Computer, Inc.  All rights reserved.
        !            26:  *
        !            27:  *      File:  machdep/ppc/libc/ffs.s
        !            28:  *
        !            29:  *     int ffs(int value)
        !            30:  *
        !            31:  *     DESCRIPTION
        !            32:  *             The ffs() function finds the first bit set in value and returns the
        !            33:  *             index of that bit.  Bits are numbered starting from 1, starting at
        !            34:  *             the right-most bit. A return value of 0 means that the argument was
        !            35:  *
        !            36:  * HISTORY
        !            37:  *     14-Aug-1998     Umesh Vaishampayan      ([email protected])
        !            38:  *             Optimized!
        !            39:  *
        !            40:  *  10-Mar-1998 Matt Watson ([email protected])
        !            41:  *      Correctified
        !            42:  *
        !            43:  *  19-Jan-1998 Matt Watson ([email protected])
        !            44:  *      Simplified
        !            45:  *
        !            46:  *  24-Jan-1997 Umesh Vaishampayan ([email protected])
        !            47:  *      Ported to PPC. 
        !            48:  */
        !            49: 
        !            50: .text
        !            51: .align 4
        !            52: .globl _ffs
        !            53: _ffs:                                  /* Cycles */
        !            54:        neg             r0,r3           /* 0 */
        !            55:        and             r3,r0,r3        /* 1 */
        !            56:        li              r4, 32          /* 1 */
        !            57:        cntlzw  r3,r3           /* 2 */
        !            58:        subf    r3,r3,r4        /* 3 */
        !            59:        blr

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