bsd/dev/ppc/ffs.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_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 License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28 /* Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved.
  29  *
  30  *      File:   machdep/i386/libc/ffs.c
  31  *      Author: Bruce Martin, NeXT Computer, Inc.
  32  *
  33  *      This file contains machine dependent code for the ffs function
  34  *      on NeXT i386-based products.  Currently tuned for the i486.
  35  *
  36  * HISTORY
  37  * 27-Sep-92  Bruce Martin (Bruce_Martin@NeXT.COM)
  38  *      Created: stolen from Mike's code.
  39  */
  40
  41 unsigned
  42 ffs(unsigned mask)
  43 {
  44         unsigned bitpos;
  45
  46         if (mask == 0)
  47                 return 0;
  48
  49         bitpos = 1;
  50         while ((mask & 0xff) == 0) {
  51                 bitpos += 8;
  52                 mask >>= 8;
  53         }
  54         while ((mask & 1) == 0) {
  55                 bitpos += 1;
  56                 mask >>= 1;
  57         }
  58         return bitpos;
  59 }