libkern/i386/OSAtomic.s

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_OSREFERENCE_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
  10  * License may not be used to create, or enable the creation or
  11  * redistribution of, unlawful or unlicensed copies of an Apple operating
  12  * system, or to circumvent, violate, or enable the circumvention or
  13  * violation of, any terms of an Apple operating system software license
  14  * agreement.
  15  *
  16  * Please obtain a copy of the License at
  17  * http://www.opensource.apple.com/apsl/ and read it before using this
  18  * file.
  19  *
  20  * The Original Code and all software distributed under the License are
  21  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  22  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  23  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  24  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  25  * Please see the License for the specific language governing rights and
  26  * limitations under the License.
  27  *
  28  * @APPLE_LICENSE_OSREFERENCE_HEADER_END@
  29  */
  30
  31 #;**************************************************************************
  32 #;* Boolean OSCompareAndSwap(SInt32 oldValue, SInt32 newValue, SInt32 * ptr) *
  33 #;**************************************************************************
  34
  35         .globl _OSCompareAndSwap
  36
  37 _OSCompareAndSwap:
  38         movl             4(%esp), %eax  #; oldValue
  39         movl             8(%esp), %edx  #; newValue
  40         movl            12(%esp), %ecx  #; ptr
  41         lock
  42         cmpxchgl        %edx, 0(%ecx)   #; CAS (eax is an implicit operand)
  43         sete            %al                             #; did CAS succeed? (TZ=1)
  44         movzbl          %al, %eax               #; clear out the high bytes
  45         ret