[FFmpeg-devel] [PATCH/RFC] ALT_BITSTREAMREADER optimizations for the platforms with strict alignment

Siarhei Siamashka siarhei.siamashka
Mon Dec 8 23:35:54 CET 2008

On Tuesday 09 December 2008, Siarhei Siamashka wrote:
> A32_BITSTREAM_READER is not very good overall, because it blows up code
> size too much, wasting precious space in L1 cache. I remember it was set as
> default for ARM after running some benchmarks with ffmp3 decoder. Appears
> that it is quite good for MP3 decoder code because this decoder has a lot
> of small constant size calls to 'get_bits' function (for which UPDATE_CACHE
> from A32_BITSTREAM_READER is mostly only doing counter check and a
> conditional jump over the rest of code).

... or alternatively ffmp3 can be optimized to use low level bitstream reader
API (UPDATE_CACHE/SHOW_BITS/... macros) and eliminate a lot of excessive cache
update operations completely. That would also make A32_BITSTREAM_READER not so
useful here.

Best regards,
Siarhei Siamashka

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