RE: [Caml-list] 32 bit floats, SSE instructions

["Brandon J. Van Every" <vanevery@indiegamedesign.com>]

Christophe TROESTLER wrote:
>
> If you need a selected number of routines using 32 bits floats,
> implement them in C and interface them to OCaml.  But this could be
> slow depending of what you want to do -- i.e. maybe you want to use
> OCaml for higher level stuff?  Could you please provide more details ?

A 3D graphics guy has to contend with a large number of numeric
problems.  Some of them are cut, dried, and repetitive enough to justify
coding up a C routine for them.  For example, transforming a large
number of XYZW vectors by a 4x4 matrix is a 'pat' problem that occurs at
some point in 3D graphics processing.

However, lotsa 3D problems are exploratory in nature.  For those you
want to use an efficient high level language, i.e. OCaml.  You'd like to
code it up once, have it be pretty fast, and not ever worry about
futzing with C <--> OCaml bureaucracy.  There isn't necessarily an
'array version' of the problem, and you may not wish to figure it out in
any event.  C interfaces carry overhead, i.e. you'd rather have stuff go
straight down to machine code without any function calls, if all you're
doing is twiddling a few floats.

Basically it's not an answer to say "Ah, yes, look at this great
language OCaml!" when in practice all you're ever doing is writing C.

I'm not exactly sure why language designers think 32 bit floats "don't
count."  Quite a number of high level languages make the choice of
blowing them off.  I guess quite a lot of high level languages aren't
interested in widespread industrial application, just ease of compiler
implementation.  The reality is that 32 bit floats get used in the real
world all over the place by 3D graphics guys.  That has something to do
with it being a core capability of many CPUs and an IEEE standard.  64
bit floats cost twice as much memory, are much slower for division and
square rooting, and in many applications the extra precision is not
needed.

The last time I tried to talk about 32 bit floats with 'language guys'
was the Python crowd.  Generally speaking, that community doesn't have a
clue about performance, and hasn't coughed up any significant 3D
graphics work either.


Cheers,                     www.indiegamedesign.com
Brandon Van Every           Seattle, WA

"The pioneer is the one with the arrows in his back."
                          - anonymous entrepreneur



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