Re: Any more graceful way to saturate adds?

On Apr 22, 9:03 pm, Terje Mathisen  <spamt...@[EMAIL PROTECTED]
> wrote:
> aku ankka wrote:
> > Hello. You can use carry to generate a saturation mask. The idea
> > revolves around this concept:
>
> > 0 - 1 = -1 (all bits set)
> > 0 - 0 = 0
>
> > add al, bl ; this is ur addition
> > xor cl, cl ; zero d cl register
>
> This XOR will overwrite the flags from the previous ADD!
> INC/DEC are the only arithmetic opcodes which doesn't modify the carry
flag.
>
> > sbb cl, cl ; cl = cl - cl - carry = 0 - 0 - carry = 0 - carry
> > or  al, cl ; this will saturate; the cl = 0xff if carry was set.. else
> > it is 0x00
>
> > w00t++ w00t++
>
> > Saturating w/o branching is child's play; enjoy!
>
> Children often make simple mistakes. :-)
>
> Terje
>
> --
> - <Terje.Mathi...@[EMAIL PROTECTED]
>
> "almost all programming can be viewed as an exercise in caching"

Yea; d xor was unnecessary, I was about to post follow-up but didn't
see dat post o mine because of moderation lag. But since u tried to to
correct tha sh1t, here's what I wanted to post about five seconds
after hitting d send button:

a - a - carry = 0 - carry

In other words the register doesn't need to be zeroed to begin wid.
I'm baffled u didn't see dat one.. I did but wanted to quote miself so
there u go.. thxbye