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

[Yann Guidon <whygee@f-cpu.org>]

hi,

nico wrote:

> On 09 Jan 2003 20:52:34 +0100
> Antoine <antoine@rezo.net> wrote:
>
> > Hi,
> >
> > Le ven 10/01/2003 à 21:37, nico a écrit :
> >    
> > > Just a stupid question : is 8 bits integer mode usefull ?
> > >      
> > I think so ;)
> >    
idem :-)

> > > "Char" C type are going to be 16 bits (unicode)
> > >      
> > The most widely used encoding of unicode, UTF-8, is based on regular
> > bytes (it's a variable length encoding backwards compatible with
> > Ascii). That means both legacy character strings and unicode strings 
> > will use byte operations. Protocol networks, compression formats will 
> > also remain byte-based. And so on ;)
> >
> >    
> > > Gimp use 16 bit per channel
> > >      
> > I think that's false, that's even why Film Gimp exists (movie guys
> > need more than 8 bits per channel and Gimp can't satisfy their needs).
> > However even if Gimp can do 16 bits per channel, most images will
> > still only require 8 bits per channel, leading to more compact
> > representations and faster calculations (and less memory transfers
> > ;-)).
> >
> > Also if you think SIMD in stuff like GIMP, operations with 8-bit
> > per channel will be twice faster than with 16-bit channel (because
> > your registers have a fixed size and you can stuff twice more bytes
> > than 16-bit integers into a register).
> Half the bandwith consumption but many more operations to avoid
> overflow/underflow problems ! I beleive that GPU use float to avoid such
> mess !
>  
what ? you think that your grarphic card transforms the bytes into 
floats for display
and storage ? AFAIK, with GIMP and most other software, bytes remain bytes.
It becomes critical only when your card performs 2D and 3D operations itself
for games and acceleration : texture mapping, bump mapping, filtering....
It is NOT the purpose of the PC software to do these heavy computations
that now involve filtering and other math stuffs. What you provide to 
your board
is a set of coordinates and textures, that's all.


> > Hey, if you wanna write an x86 emulator for F-CPU, you'll also need 
> > bytes :-)))
> hugh.. !
>  
and i think that even writing a device driver or using a Unix-like 
kernel involves
a LOT of chars. even if the consoles are slowly interpreting unicode,
the kernel still deals with error messages in dumb ASCII.

> > Regards
> >
> > Antoine.
> >    
YG

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