libkern/i386/OSAtomic.s

   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
  23 #;**************************************************************************
  24 #;* Boolean OSCompareAndSwap(SInt32 oldValue, SInt32 newValue, SInt32 * ptr) *
  25 #;**************************************************************************
  26
  27         .globl _OSCompareAndSwap
  28
  29 _OSCompareAndSwap:
  30         #; this is _lame_, the project will not currently accept asm code that
  31         #; requires anything beyond a 386, but that chip:
  32         #; - does not support MP
  33         #; - does not support the cmpxchgl instruction
  34         #; - does not support the lock meta-instruction
  35         #; so what is a poor guy to do?  comment it out...
  36         pushl           %edi
  37         pushl           %esi
  38         movl            0+8+4(%esp),%eax        #; oldValue
  39         movl            4+8+4(%esp),%edi        #; newValue
  40         movl            8+8+4(%esp),%esi        #; ptr
  41         lock
  42         cmpxchgl        %edi,0(%esi)            #; CAS (eax is an implicit operand)
  43         sete            %al                                     #; did CAS succeed? (TZ=1)
  44         andl            $0x000000ff,%eax        #; clear out the high bytes (has to be an easier way...)
  45         popl            %esi
  46         popl            %edi
  47         ret
  48