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Annotation of XNU/libkern/i386/OSAtomic.s, revision 1.1

1.1     ! root        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: 

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