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Rep:Re: [f-cpu] Are 8 bits SIMD mode usefull ?



I beleive they are some mix.

Sparc/Mips and i beleive all RISC processor didn't have any 8 bits load
(nor 16 bits). They just manipulate 32 or 64 bits at the same time but
still handle C "char". 

I am pretty sure that's x86 is the only cpu that could fetch 8 or 16
bits from the memory (which make the LSU complexe).

The other problem are the usefullness of a 8 bits vector. I know that
picture use this size a lot but it need so much trick ! (i had followed
ffmpeg that made a great MMX FFT code, but there are some problem of
darkness or gain in it). The only use could be the convertion between
picture type (RGB, BGA, YUV420,YUV420P,YUV422,...) but video card will
handle it more and more !

---
GPU use "128 bits pixel" to enable pixel and virtex shader. Very few
instructions could be handle (~128) per pixel/vertex. I could imagine
the udge pipeline that is could be. That's the famous DirectX 9.0
advantage (from 8 bits to 24 bits float for some part in the >9500 ATI
card, then (GeoforceFX ?) to full 32 bits float by channel in all the 3D
pipeline).

nicO

-----Message d'origine-----
De: Michael Riepe <michael@stud.uni-hannover.de>
A: f-cpu@seul.org
Date: 10/01/03
Objet: Re: [f-cpu] Are 8 bits SIMD mode usefull ?

On Fri, Jan 10, 2003 at 08:37:07PM +0000, nico wrote:
> Just a stupid question : is 8 bits integer mode usefull ?

Yes!

> "Char" C type are going to be 16 bits (unicode) or even 32. 3D are
going
> in floating point even in the GPU. Gimp use 16 bit per channel (in
> certain mode, even more ?). 

What you mean is `wchar_t', not `char'. And even that can be encoded
in a series of bytes (that's called UTF-8).

8-bit mode isn't dead. I guess it will never die.

-- 
 Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
 "All I wanna do is have a little fun before I die"
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