[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: EU Report (was: Re: [f-cpu] Register set revised)



> What exactly is the SAD insn supposed to do?

Sum of Absolute Differences. It take two SIMD words, makes
abs(a-b) for each corresponding bytes and adds all these differences.
This is used when computing motion vectors in mpeg encoder.
I've seen it in several instruction sets. However I don't know where
it is usable outside of mpeg.

> 	tmp = A ą (B + lsb(C))
> 	Y = tmp % pow(2, chunksize)
> 	Z = tmp / pow(2, chunksize)
>
> Since that's a 3r2w operation, don't expect it to be implemented in FC0.
> It would be quite useful for adding/subtracting big numbers, however.

seems useful. Big number libs (gmp, rsalib...) often need to resort
to some trick most related to carry propagation. In GMP manual
there is many info on the topic.

Would not be possible to do CMP in ASU too ? Both are working
with "propagating" information from LSB toward MSB ...
Or other question, is the new source available ? I'd like to
take a look :)

devik

*************************************************************
To unsubscribe, send an e-mail to majordomo@seul.org with
unsubscribe f-cpu       in the body. http://f-cpu.seul.org/