[FFmpeg-devel] VP8 decoder optimization status

[Jason Garrett-Glaser]

On Wed, Jun 30, 2010 at 1:19 PM, Stefan Gehrer <stefan.gehrer at gmx.de> wrote:
> On 06/30/2010 10:15 PM, Stefan Gehrer wrote:
>>
>> 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;
>
> 3. shift = ff_h264_norm_shift_old[c->high] + 1;
>
> as c->high should never become zero.

This sounds like the best option: 1) is 3 ops on x86 minimum, as is
2).  3) is at most two ops.

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