[MPlayer-dev-eng] [PATCH] Stereo3D: Row-Interleave Output Support

[Reimar Döffinger]

On Tue, Jun 21, 2011 at 04:09:30PM -0400, Steaphan Greene wrote:
> On 06/21/2011 03:58 PM, Reimar Döffinger wrote:
> > On Tue, Jun 21, 2011 at 02:08:58PM -0400, Steaphan Greene wrote:
> >> So, I would expect calling memcpy_pic for the first copy would actually
> >> end up being slower than the version you just committed, despite the
> >> additional instructions required to skip these unused rows.
> >>
> >> Dos that sound right to you?
> > 
> > I think that is in principle what will happen (I haven't checked
> > though), however the semantics aren't that that the memcpy_pic
> > _has_ to copy all "extra" bytes, it could just copy e.g. 8 extra
> > bytes to reach a multiple of 16 to allow faster copying via
> > some instruction that copies 16 bytes at a time.
> > The memcpy_pic2 version with "1" as last argument will always
> > have to copy those last 8 bytes with something else.
> 
> The way memcpy_pic2 (the actual inline function in both cases) is
> written now, without the 1, it assumes that two with the same stride are
> contiguous copies (it does not account for row-skipping), so it will
> copy all the extra data by combining the row copies into a single
> fast_memcpy() call for the whole frame (or half-frame).
> 
> I agree with you, though.  It COULD be written to better optimize this
> case.  It just isn't now, and changing those core functions seemed like
> a very bad idea for just this one output case.

No disagreement though, I was mostly curious if we agree that for fixing
bugs it would have been enough to change the second one, and changing
the first one is basically just an optimization.