[FFmpeg-devel] [PATCH 3/4] VP8: token probs doesn't need padding

[Måns Rullgård]

Jason Garrett-Glaser <darkshikari at gmail.com> writes:

> 2011/3/11 M?ns Rullg?rd <mans at mansr.com>:
>> Jason Garrett-Glaser <jason at x264.com> writes:
>>
>>> prob[0] is the only prob array ever accessed, so prob[1] can serve as padding
>>> for prob[0].
>>> ---
>>> ?libavcodec/vp8.h | ? ?3 +--
>>> ?1 files changed, 1 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/libavcodec/vp8.h b/libavcodec/vp8.h
>>> index d3b8705..b94d453 100644
>>> --- a/libavcodec/vp8.h
>>> +++ b/libavcodec/vp8.h
>>> @@ -233,8 +233,7 @@ typedef struct {
>>> ? ? ? ? ?uint8_t golden;
>>> ? ? ? ? ?uint8_t pred16x16[4];
>>> ? ? ? ? ?uint8_t pred8x8c[3];
>>> - ? ? ? ?/* Padded to allow overreads */
>>> - ? ? ? ?uint8_t token[4][17][3][NUM_DCT_TOKENS-1];
>>> + ? ? ? ?uint8_t token[4][16][3][NUM_DCT_TOKENS-1];
>>> ? ? ? ? ?uint8_t mvc[2][19];
>>> ? ? ?} prob[2];
>>> ?} VP8Context;
>>
>> If only one is accessed, why are there two?
>
> The second is a backup.  If update_probabilities = 0, the
> probabilities used for the current frame are thrown away after
> decoding it.  So we copy the old probabilities to prob[1], use prob[0]
> for the current frame, then restore them afterward.

OK with me then.

-- 
M?ns Rullg?rd
mans at mansr.com