[FFmpeg-soc] AAC integration

[Andreas Öman]

Andreas Öman wrote:
> Michael,
> 
> I'm quite satisfied with the shape of the AAC-LC decoder now.

I've done various performance benchmarks at some interesting places
and might as well comment on it right away.

==========================
ivquant():

This is called quite often and therefore pow() is accelerated with
a table:

Increasing the table size wont gain much speed:

table size 8192:
700 dezicycles in ivquant, 16777086 runs, 130 skips

table size 512:
701 dezicycles in ivquant, 16777084 runs, 132 skips

original: (256 entries)
702 dezicycles in ivquant, 16777089 runs, 127 skips

table size 32:
707 dezicycles in ivquant, 16777088 runs, 128 skips

table size 1:
1694 dezicycles in ivquant, 16776923 runs, 293 skips


==========================
vector_fmul_add_add_add()

There is a suggestion to move this into dsputil(), but i'll
rather await your comment on the subject.

It's only used by the short window transform (which are used
relatively seldom)

I wrote an pure SSE-version of it, and ...

SSE: 247843 dezicycles in eight short sequence, 1024 runs, 0 skips
current: 257722 dezicycles in eight short sequence, 1024 runs, 0 skips

... as you can see the speed gain is just a few percent.

Since it's seldom used the speed gain isn't even measurable on a
whole file (2-3 minutes of audio)