[FFmpeg-devel] AAC decoder round 5

[Michael Niedermayer]

On Fri, Aug 08, 2008 at 07:59:35PM +0100, Robert Swain wrote:
> 2008/8/8 Michael Niedermayer <michaelni at gmx.at>:
> > On Fri, Aug 08, 2008 at 03:38:06PM +0100, Robert Swain wrote:
> >> 2008/8/8 Robert Swain <robert.swain at gmail.com>:
> >>
> >> [...]
> >>
> >> > So, it seems the issue is not MAX_CHANNELS so much as the window group
> >> > and scalefactor band arrays. I'm going to check the cases for maximum
> >> > number of scalefactor bands per window group as I expect it may be
> >> > beneficial to flatten these two indices.
> >>
> >> const uint8_t ff_aac_num_swb_1024[] = {
> >>     41, 41, 47, 49, 49, 51, 47, 47, 43, 43, 43, 40
> >> };
> >>
> >> const uint8_t ff_aac_num_swb_128[] = {
> >>     12, 12, 12, 14, 14, 14, 15, 15, 15, 15, 15, 15
> >> };
> >>
> >> For the long transform, there can only be 1 window group so the worst
> >> case there is 51 scalefactor bands in total.
> >>
> >> For the short transform there can be up to 8 window groups (i.e. each
> >> group containing only one short window) each with up to 15 scalefactor
> >> bands, totalling 120 scalefactor bands maximum for this case.
> >>
> >> So, instead of [8][64] we could have [120] which is quite a bit better
> >> but maybe it would obfuscate the code a lot, I'll ponder this now. At
> >> the very least we can have [8][51]. :)
> >
> > [8][51].might lead to slow addressing of the contents due to *51 instead
> > of <<6
> 
> See attached.
> 
> Reduces ChannelElement to 42672 from 80688 bytes, SingleChannelElement
> to 16896 from 21600 bytes and ChannelCoupling to 8744 from 36968
> bytes.

great,patch ok

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No great genius has ever existed without some touch of madness. -- Aristotle
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