bsd/dev/ppc/ffs.c

   1 /*
   2  * Copyright (c) 2006 Apple Computer, Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_OSREFERENCE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License.  The rights granted to you under the
  10  * License may not be used to create, or enable the creation or
  11  * redistribution of, unlawful or unlicensed copies of an Apple operating
  12  * system, or to circumvent, violate, or enable the circumvention or
  13  * violation of, any terms of an Apple operating system software license
  14  * agreement.
  15  *
  16  * Please obtain a copy of the License at
  17  * http://www.opensource.apple.com/apsl/ and read it before using this
  18  * file.
  19  *
  20  * The Original Code and all software distributed under the License are
  21  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  22  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  23  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  24  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  25  * Please see the License for the specific language governing rights and
  26  * limitations under the License.
  27  *
  28  * @APPLE_LICENSE_OSREFERENCE_HEADER_END@
  29  */
  30 /* Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved.
  31  *
  32  *      File:   machdep/i386/libc/ffs.c
  33  *      Author: Bruce Martin, NeXT Computer, Inc.
  34  *
  35  *      This file contains machine dependent code for the ffs function
  36  *      on NeXT i386-based products.  Currently tuned for the i486.
  37  *
  38  * HISTORY
  39  * 27-Sep-92  Bruce Martin (Bruce_Martin@NeXT.COM)
  40  *      Created: stolen from Mike's code.
  41  */
  42
  43 unsigned
  44 ffs(unsigned mask)
  45 {
  46         unsigned bitpos;
  47
  48         if (mask == 0)
  49                 return 0;
  50
  51         bitpos = 1;
  52         while ((mask & 0xff) == 0) {
  53                 bitpos += 8;
  54                 mask >>= 8;
  55         }
  56         while ((mask & 1) == 0) {
  57                 bitpos += 1;
  58                 mask >>= 1;
  59         }
  60         return bitpos;
  61 }