[FFmpeg-devel] Yellow fever

[Måns Rullgård]

Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:

> On Sat, Aug 21, 2010 at 10:12:35AM +0100, M?ns Rullg?rd wrote:
>> As you all have no doubt completely ignored, FATE turned much more
>> yellow yesterday.  The reason for this is that I disabled unaligned
>> memory access fixup on those machines which do not support it in
>> hardware (Alpha, ARMv5, MIPS).  Most of these are failing a single
>> test: lavfi-pixfmts_scale_le.
>> 
>> The problem here is btr32ToY() and related functions in libswscale:
>> 
>> #define BGR2Y(type, name, shr, shg, shb, maskr, maskg, maskb, RY, GY, BY, S)\
>> static inline void name(uint8_t *dst, const uint8_t *src, long width, uint32_t *unused)\
>> {\
>>     int i;\
>>     for (i=0; i<width; i++) {\
>>         int b= (((const type*)src)[i]>>shb)&maskb;\
>>         int g= (((const type*)src)[i]>>shg)&maskg;\
>>         int r= (((const type*)src)[i]>>shr)&maskr;\
>> \
>>         dst[i]= (((RY)*r + (GY)*g + (BY)*b + (33<<((S)-1)))>>(S));\
>>     }\
>> }
>> 
>> These functions are called from hyscale(), like this:
>> 
>> static inline void RENAME(hyscale)(SwsContext *c, uint16_t *dst, long dstWidth, const uint8_t *src, int srcW, int xInc,
>>                                    const int16_t *hLumFilter,
>>                                    const int16_t *hLumFilterPos, int hLumFilterSize,
>>                                    uint8_t *formatConvBuffer,
>>                                    uint32_t *pal, int isAlpha)
>> {
>>     void (*toYV12)(uint8_t *, const uint8_t *, long, uint32_t *) = isAlpha ? c->alpToYV12 : c->lumToYV12;
>>     void (*convertRange)(uint16_t *, int) = isAlpha ? NULL : c->lumConvertRange;
>> 
>>     src += isAlpha ? c->alpSrcOffset : c->lumSrcOffset;
>> 
>>     if (toYV12) {
>>         toYV12(formatConvBuffer, src, srcW, pal);
>>         src= formatConvBuffer;
>>     }
>> [...]
>> }
>> 
>> c->lumSrcOffset is either 1 or -1, meaning src will _always_ be
>> unaligned.
>
> Not that it makes much of a difference overall, but I think you
> are mistaken there (or I misunderstood you).
> c->lumSrcOffset is one for PIX_FMT_RGB48LE, and 1 or -1 for the
> 32_1 formats, but 0 for the other cases.
> So only these (rather uncommon formats) need a fix, and IMO
> for those even a solution with bad performance would be ok.

I didn't dig very deeply, but it is 1 or -1 in the test that's
failing, and that's bad enough.  How would you propose fixing it?

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