libkern/i386/OSAtomic.s

   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
  26 #;**************************************************************************
  27 #;* Boolean OSCompareAndSwap(SInt32 oldValue, SInt32 newValue, SInt32 * ptr) *
  28 #;**************************************************************************
  29
  30         .globl _OSCompareAndSwap
  31
  32 _OSCompareAndSwap:
  33         #; this is _lame_, the project will not currently accept asm code that
  34         #; requires anything beyond a 386, but that chip:
  35         #; - does not support MP
  36         #; - does not support the cmpxchgl instruction
  37         #; - does not support the lock meta-instruction
  38         #; so what is a poor guy to do?  comment it out...
  39         pushl           %edi
  40         pushl           %esi
  41         movl            0+8+4(%esp),%eax        #; oldValue
  42         movl            4+8+4(%esp),%edi        #; newValue
  43         movl            8+8+4(%esp),%esi        #; ptr
  44         lock
  45         cmpxchgl        %edi,0(%esi)            #; CAS (eax is an implicit operand)
  46         sete            %al                                     #; did CAS succeed? (TZ=1)
  47         andl            $0x000000ff,%eax        #; clear out the high bytes (has to be an easier way...)
  48         popl            %esi
  49         popl            %edi
  50         ret
  51