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Annotation of kernel/machdep/ppc/libc/ffs.s, revision 1.1.1.1

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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