[FFmpeg-devel] [PATCH] [RFC] Second try at pixdesc.h:write_line()

[Stefano Sabatini]

On date Sunday 2009-04-19 15:56:10 +0200, Michael Niedermayer encoded:
> On Sun, Apr 19, 2009 at 12:35:44PM +0200, Stefano Sabatini wrote:
> > Mmh what about this?
> > 
> >         while (w--) {
> >             *p |= *src++ << (8 - depth + shift);
> >             shift -= step;
> >             p -= shift >> 3;
> >             shift &= 7;
> >         }
> > 
> > I'm not still sure it is what you meant.  Also AFAIU this can only
> > work for a pixel depth of 1, while pixel/source can contain pixels
> > with a depth up to 16 bits (uint16_t).
> > 
> > Note that I cannot shift for a negative value (result is undefined).
> 
> i meant what i wrote
> *p |= *src++ << shift;
> 
> and 
> shift &= 7; done priorly in all cases makes sure this is not negative
> so i am no sure what you meant
> did i miss something ?
> 
> and yes it of course wont work with >8bit per sample or where a sample
> crosses a byte boundary but i dont think there are any pixel formats that
> would use the bitstream case and require these that we want to support.
> If you know of a specific example pixel format that would fail and that
> actually exists iam interrested ...

OK, thanks, it was exactly this which was puzzling me, maybe we should
add a notice to the docs saying something like:

"read_line() will not work with bitstream formats with a depth per
sample greater than 8, or where a sample crosses a byte boundary."

I'm attaching the updated hflip filter patch, which I'm using to test
it (togheter with the pixdesc definition already posted).

Regards.
-- 
FFmpeg = Foolish Fostering Multimedia Portable Ecumenical Game
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