[vorbis-dev] FLOOR_fromdB_LOOKUP

[Gian-Carlo Pascutto]

> Hello,
> You know, I always worry about the precision
> and the float constants... and there is a large
> lookup table in the floor1.c ... and I figure out
> a way to keep the code size and speed, but
> to improve the precision at this lookup table.
> (the difference is small, but audible)
> 
> Here is the modifications in the floor1.c:
> 
> static unsigned long FLOOR_fromdB_LOOKUP[256]={
> 0x33E4B434,0x33F390FF,0x3401B286,

[snip] 

>   d[x]*=*((float *)&FLOOR_fromdB_LOOKUP[y]);

Hmm, doesn't this trick depend on float representation
within the CPU, and hence is inherently nonportable?

Also, AFAIK float only guarantees 7 significant digits. 
The constants in the current source all have at least 8, so 
they should be safe.

I don't really understand how this could make a
difference, let alone an audible one.


-- 
GCP

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