bsd/dev/ppc/ffs.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /* Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved.
  23  *
  24  *      File:   machdep/i386/libc/ffs.c
  25  *      Author: Bruce Martin, NeXT Computer, Inc.
  26  *
  27  *      This file contains machine dependent code for the ffs function
  28  *      on NeXT i386-based products.  Currently tuned for the i486.
  29  *
  30  * HISTORY
  31  * 27-Sep-92  Bruce Martin (Bruce_Martin@NeXT.COM)
  32  *      Created: stolen from Mike's code.
  33  */
  34
  35 unsigned
  36 ffs(unsigned mask)
  37 {
  38         unsigned bitpos;
  39
  40         if (mask == 0)
  41                 return 0;
  42
  43         bitpos = 1;
  44         while ((mask & 0xff) == 0) {
  45                 bitpos += 8;
  46                 mask >>= 8;
  47         }
  48         while ((mask & 1) == 0) {
  49                 bitpos += 1;
  50                 mask >>= 1;
  51         }
  52         return bitpos;
  53 }