Re: Any more graceful way to saturate adds?

On Apr 15, 12:11 am, pete <spamt...@[EMAIL PROTECTED]
> wrote:
> Just to be absolutely clear about the problem (and without any
> attempt at optimizing the code), can you confirm that the below
> is what you're after?
>
> (unsigned sample in DL, signed "update" in AL)
>
>         sub  dh, dh             ;DH = 0
>         cbw                     ;sign-extend AL to AX
>         add  dx, ax             ;signed addition
> Now:
>         if DH == 0, nothing to do: ans in DL
>         if DH == FF, -ve overflow so clamp to 0: set DL = 0
>         if DH == 1, +ve overflow so clamp to FF: set DL = FF
>
> Is that correct?

Yes, that's exactly correct.  My beginner's attempt at applying the
clamping has been done with JMPs, which are really costly in an inner
loop (especially on my lowly 808x) and I feel that I'm missing
something obvious.

Was Terje's solution:

  add dl,al     ; Carry set if it overflows!
  sbb al,al     ; AL = 0xff if overflow
  or dl,al      ; Turns any overflow into 0xff

....the right one?  I see overflow handling but not underflow...