[vorbis-dev] encoder optimization

[Segher Boessenkool]

Hello again,

The single most expensive function (on intel x86) is seed_curve() ;
the expensive part is todB():

#define todB(x)   ((x)==0?-9.e40:log(fabs(x))*8.6858896)

We don't need all this precision:

int choice=(int)((todB(amp)-specmax+specatt)/10.-1.5);

Simplest, fastest way is only portable over ieee[78]54 fp:
take a bitmask over amp, do some right shift, do a table lookup.

This should save ~ 25-30%

If no-one else implements it, I will; just wait a few days, I'm afraid.

Bye bye,

Segher

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/