Re: A86: sub
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Re: A86: sub
if by 'bit' you mean 16-bit piece, yes.
you can subtract 32-bit values like this:
; src = src - dest
sub32: ld hl,(srclow)
ld de,(destlow)
or a ; clear the carry flag
sbc hl,de ; subtract low 16 bits
ld (srclow),hl ; store low result
ld hl,(srchigh)
ld de,(desthigh)
sbc hl,de ; subtract high 16 bits and carry
ld (srchigh),hl ; store high result
ret
srclow: .dw 0
srchigh: .dw 0
destlow: .dw 0
desthigh: .dw 0
(remember to store something into the src and dest first!)
this can be extened to as large as you want, but unless you need really
fast math, or more precision than they offer, i'd work with the op
registers for anything more than that.
and if you were really going for high speed and low space, you could use
self modifying code and store the src and dest in the opcodes that load
them into the registers...
-josh
On Sat, 18 Sep 1999 04:20:13 GMT "Andrew T" <ironman_294@hotmail.com>
writes:
>
>Ok I might have to subtract numbers that take up more mem then 16
>bits. And
>as I thought about it I came up with takeing one bit at a time and
>subtracting them. Will this work or am I just out of my mind (if I am
>right
>would I use the carry flag or not).
>
>Thanx
>Andrew
>
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