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



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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