Re: MMX speedup for Floyd Steinberg error diffusion

"Maarten Kronenburg"  wrote in message
>
> The 4 32-bit words can be stored in a single 128-bit xmm register.
> Then you copy and ****ft left and add/subtract, because
> 7 = 8 - 1 = 2^3 - 1 and 5 = 4 + 1 = 2^2 + 1 etc.
> Then you ****ft right because 16 = 2^4.
> The ****ft is the PSLLD/PSRLD and the add/subtract is the PADDD/PSUBD.
> The reference for these instructions are in:
> http://developer.intel.com/products/processor/manuals/index.htm
> see instruction set reference.
> The timings can be found in:
> http://agner.org/optimize/

In addition to this:
In order not to loose the 3 highest bits, the process must be scaled down
3
bits, that is ****ft right 3 bits, do the thing, and then ****ft left 3 bits
again. Then of course some ****fts cancel out.
Maarten.