[vorbis-dev] New LSP code committed

[Monty]

> How are you going to do the fromdB() without using exp()? Couldn't figure
> out how to factor out the fromdB() after the lsp_to_curve(). Are you
> doing the fromdB by table lookup or something? I guess that is worse...

I was going to make table lookup an option to replace everything past the p/q
multiplicitive sum loop and before the residue dot product, yes (probably
software selectable as a 'fast' mode.  For fixed point projects, the lookup
would be essential). As the usable range is only about 140dB, a fairly fine
grained lookup would not be exhorbitant, and a granularity of 1dB is still
acceptible for most purposes. We could even interpolate the lookup for extra
precision, as I'll be doing to replace cos() in lsp_to_curve (the cos() call
there uses exceptionally fine angles, but the actual precision of the
instantaneous slope of the cos() function isn't really that important.  A
linearly interpolated 128 entry cos() lookup adds less than .01 dB of
inaccuracy in my empirical testing, but that interpolation is essential!)

> vorbis decoding uses too much memory at the moment (cache wars). Maybe
> some pipelining will help.

Yes, it's true.  Alot of that is poorly organized lookups. Precomputation 
isn't always a win... :-(

Monty

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