Absolute value

[ChimpFace9000]

How do i get the absolute value of a number? I thought maybe there was an instruction that did it, but i couldnt find one.

[Knight_Vision]

Hehe... I was wondering that myself.. LOL

I'm still learning. There is Soooo much in assembly to learn.. uhhgg...

[jim mcnamara]

I haven't coded this stuff for long time, and I don't have MASM anymore. Please just take this as an explanation. I'm not sure about parts of this. But, I'm very sure the part from START thru $RESTORE is correct.

The algorithm for abs is
compare value to zero
jump to return if true
neg the value
return:
put value in eax

Here's a *** version for returning the abs of an integer -
but you'll get the idea.

PUBLIC	?abs					; abs
_TEXT	SEGMENT
_a = 8                                   
?absi PROC NEAR					; abs
; abs function for integers only

	push	ebp                              ; preserve it
	mov	ebp, esp                         ; get passed value location (frame)
	sub	esp, 64			        
	push	ebx
	push	esi
	push	edi
	lea	edi, DWORD PTR [ebp-64]
	mov	ecx, 16				
	mov	eax, -858993460			
	rep stosd
$START:
       mov   eax, DWORD PTR _a[ebp]      ; place value in eax
	cmp	eax, 0                              ; is it > = 0
	jl	SHORT $MINUS                        ; no
	jmp	SHORT $RESTORE                      ; yes, return
$MINUS:
	neg	eax                                 ; value * -1     
$RESTORE:
	pop	edi
	pop	esi
	pop	ebx
	mov	esp, ebp
	pop	ebp
	ret	0
?absi ENDP					; abs1
_TEXT	ENDS
END