Re: [Nasm-users] Setting/Clearing OF

[H. P. A. <hp...@zy...>]

On 08/10/2009 10:54 PM, Frank Kotler wrote:
> 
> "lahf" is only going to get the low 8 bits of the flags register, and OF 
> is bit 11, so you'll have to resort to pushf, manipulate the dword on 
> stack, and popf, I think. Something like this... (intended to be 
> "portable")...
> 

Another option is to perform an operation on the arithmetic flags that
affects OF, and then use LAHF/SAHF to preserve the *other* AFs:

	; Trashes AX
clear_of:
	lahf
	xor al,al	; OF <- 0
	sahf
	ret

set_of:
	lahf
	mov al,127
	inc al		; OF <- 1
	sahf
	ret

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.