[FFmpeg-devel] VP8 decoder optimization status

[Stefan Gehrer]

On 06/30/2010 08:54 PM, Jason Garrett-Glaser wrote:
> On Wed, Jun 30, 2010 at 8:55 AM, Stefan Gehrer<stefan.gehrer at gmx.de>  wrote:
>> On 06/29/2010 04:09 AM, Jason Garrett-Glaser wrote:
>>>
>>> Here's a rough guide to what's done and what needs to be done before
>>> ffmpeg's VP8 decoder is as fast as a politician running away from an
>>> ethics committee.
>>
>> [...]
>>
>>> C:
>>>
>>> Fully convert vp5/6/7/8 arithmetic coder to bytestream: eliminate the
>>> looped renormalization.
>>
>> Like attached?
>
> We should try to reuse the h264 table if possible, IMO.

If we are talking about the same table (ff_h264_norm_shift*),
it can not be used as is,
I think these are the options:

1. shift = 7 - av_log2_16bit(c->high);

2. shift = 7 - ff_log2_tab[c->high];

3. shift = ff_h264_norm_shift_old[c->high] + !!c->high;

I favored the first over the second because on platforms
with HAVE_FAST_CLZ it could be done without any table
lookup at all.

Stefan