[FFmpeg-devel] Yellow fever

[Reimar Döffinger]

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));\
>     }\
> }
> 
> BGR2Y(uint32_t, bgr32ToY,16, 0, 0, 0x00FF, 0xFF00, 0x00FF, RY<< 8, GY   , BY<< 8, RGB2YUV_SHIFT+8)
> BGR2Y(uint32_t, rgb32ToY, 0, 0,16, 0x00FF, 0xFF00, 0x00FF, RY<< 8, GY   , BY<< 8, RGB2YUV_SHIFT+8)
> BGR2Y(uint16_t, bgr16ToY, 0, 0, 0, 0x001F, 0x07E0, 0xF800, RY<<11, GY<<5, BY    , RGB2YUV_SHIFT+8)
> BGR2Y(uint16_t, bgr15ToY, 0, 0, 0, 0x001F, 0x03E0, 0x7C00, RY<<10, GY<<5, BY    , RGB2YUV_SHIFT+7)
> BGR2Y(uint16_t, rgb16ToY, 0, 0, 0, 0xF800, 0x07E0, 0x001F, RY    , GY<<5, BY<<11, RGB2YUV_SHIFT+8)
> BGR2Y(uint16_t, rgb15ToY, 0, 0, 0, 0x7C00, 0x03E0, 0x001F, RY    , GY<<5, BY<<10, RGB2YUV_SHIFT+7)
> 
> 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.