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x86 Assembly: How to Check for CPUID Support

An example of how to check if a processor supports the CPUID instruction.

This assembly code was compiled with MS Visual C++ Express Edition 2005 using the MACRO ASSEMBLER for MS Visual C++ Express Edition 2005.

This example is from the SSE/SSE2 tutorial.

TITLE 'extern "C" int __cdecl isCPUID();'
.686P
.model FLAT
PUBLIC	_isCPUID
_TEXT	SEGMENT
_isCPUID PROC NEAR
	
	push ebx         ; save ebx for the caller
	pushfd           ; push eflags on the stack
	pop eax          ; pop them into eax
	mov ebx, eax     ; save to ebx for restoring afterwards
	xor eax, 200000h ; toggle bit 21
	push eax         ; push the toggled eflags
	popfd            ; pop them back into eflags
	pushfd           ; push eflags
	pop eax          ; pop them back into eax
	cmp eax, ebx     ; see if bit 21 was reset
	jz not_supported
	
	mov eax, 1
	jmp exit
	
not_supported:
	xor eax, eax;

exit:
	pop ebx
	ret 0
_isCPUID ENDP
_TEXT	ENDS
END

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