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Annotation of XNU/libkern/i386/OSAtomic.s, revision 1.1.1.1

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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