bsd/dev/ppc/ffs.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /* Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved.
  26  *
  27  *      File:   machdep/i386/libc/ffs.c
  28  *      Author: Bruce Martin, NeXT Computer, Inc.
  29  *
  30  *      This file contains machine dependent code for the ffs function
  31  *      on NeXT i386-based products.  Currently tuned for the i486.
  32  *
  33  * HISTORY
  34  * 27-Sep-92  Bruce Martin (Bruce_Martin@NeXT.COM)
  35  *      Created: stolen from Mike's code.
  36  */
  37
  38 unsigned
  39 ffs(unsigned mask)
  40 {
  41         unsigned bitpos;
  42
  43         if (mask == 0)
  44                 return 0;
  45
  46         bitpos = 1;
  47         while ((mask & 0xff) == 0) {
  48                 bitpos += 8;
  49                 mask >>= 8;
  50         }
  51         while ((mask & 1) == 0) {
  52                 bitpos += 1;
  53                 mask >>= 1;
  54         }
  55         return bitpos;
  56 }