17 Sep
2002
17 Sep
'02
11:37 p.m.
On Mon, 16 Sep 2002 09:01:56 -0400
Paul Davis <pbd(a)op.net> wrote:
i thought this was pretty insightful. vst-plugins has
had a little
debate over whether or not VST should provide an integer sample
format. actually, not much of a debate. one person suggested it,
everybody else jumped on him. this post, however, is the most
detailed on why you should forget about thinking of float arithmetic
as slower than integer ...
--;p
I still use ints and fixed point because shifting and masking are
faster than fdiv and fmod.
As far as I know you cant do those instructions in one cycle using
floats, and I use them everywhere.
For my FM synth emulators I have fixed point iterators where the
integer part is shifted
and used as index to a sinetable and then the fractional part masked
for interpolation.
This amazingly beats using FSIN o my duron 850mhz, which not only
starts slowing down
when the float index is greater than PI/4, but also doesnt give good
results because
of the limited 23 bits mantisa. And yes, i tried using the fpu control
register to change
presicion to 32 bits.
Thats why my integer code is still many times faster than my floating
point code.
I allways start with floating point mixers to try out approaches and
then convert to fixed point
to gain a very considerable speed boost. Consider also that when
working with sample
data you usually have it in 16 bits signed format (uses less space
than a 32 bits floats)
Disk space and memory usage are vital when you are writing a sampler,
i'd hate it if my sample libs would take up twice as much.
Also saturated adds in MMX are awesome when layering/mixing many code
blocks.
For now, I dont see any reason to switch to floating point for my
stuff since facts show me what is
faster.
Juan Linietsky