[FFmpeg-devel] [PATCH 1/2] avcodec/vc2enc: Use LUT to assemble interleaved golomb, code

[Andreas Rheinhardt]

Lynne:
> On 12/03/2025 04:10, Andreas Rheinhardt wrote:
>> Patches attached.
>>
>> - Andreas
> 
> First patch is wild, its surprising no one considered inverting the way
> decoder parses codes for an encoder yet.

I didn't even look at the decoder.
(It is actually surprising that it took until
512e597932dfe05cf5665192efbe2c93c2e36af2 for the original code to be
improved.)

> Rather than ORing and using put_bits63, I think it would make more sense
> to write out each chunk using put_bits sequentially. It might be
> possible to reverse the lookups such that you get the MSBs first so you
> wouldn't need to reverse them out of place in a small array.
> But either way, LGTM. Feel free to explore this in a follow-up.

I don't think that writing them sequentially will improve anything: In
order to be able to use a LUT, I would have to shift the bits starting
with the MSBs into position; and then there would be the internal shifts
and checks inside put_bits().
Apart from that: put_bits63() is the same as put_bits() when BUF_BITS is
64 (see ede2b391cc516f4f93621f6a214b3410b231f582).

> 
> Second patch seems a bit pointless. It's just one single call you're
> uninlining? Chasing to save a few extra bytes of binary surely don't
> deserve having a wrapper function for uninlining.
> 

I am uninlining all calls besides the hot one. 31 callsites.
For GCC, this reduced codesize 2c36 to 25b1 (15% saved), for clang from
4b08 to 3338 (32% saved).

- Andreas