Is there an 8-bit atomic CAS (cmpxchg) intrinsic for X64 in Visual C++?
The following code is possible in 32-bit Visual Studio C++. Is there a 64-bit equivalent using intrinsics since inline ASM isn't supported in the 64-bit version of Visual Studio C++?
FORCEINLINE bool bAtomicCAS8(volatile UINT8 *dest, UINT8 oldval, UINT8 newval)
{
bool result=false;
__asm
开发者_C百科 {
mov al,oldval
mov edx,dest
mov cl,newval
lock cmpxchg byte ptr [edx],cl
setz result
}
return(result);
}
The following instrinsics compile under Visual Studio C++
_InterlockedCompareExchange16
_InterlockedCompareExchange
_InterlockedCompareExchange64
_InterlockedCompareExchange128
What I am looking for is something along the lines of
_InterlockedCompareExchange8
But that doesn't seem to exist.
No, that doesn't exist. You can implement it out-of-line though, if needed.
atomic_msvc_x64.asm
_text SEGMENT
; char _InterlockedCompareExchange8(volatile char*, char NewValue, char Expected)
; - RCX, RDX, R8
_InterlockedCompareExchange8 PROC
mov eax,r8d
lock cmpxchg [rcx],dl
ret
_InterlockedCompareExchange8 ENDP
_text ENDS
END
Verified for Visual Studio 2012 that this intrinsic does exist :
char _InterlockedCompareExchange8(volatile char*, char NewValue, char Expected)
However, it appears nowhere in the documentation.
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