[FFmpeg-cvslog] r18599 - trunk/libavcodec/xan.c

[Michael Niedermayer]

On Sat, Apr 18, 2009 at 11:08:05AM +0200, Reimar D?ffinger wrote:
> On Sat, Apr 18, 2009 at 03:34:02AM +0200, Michael Niedermayer wrote:
> > On Fri, Apr 17, 2009 at 10:07:31PM +0200, Reimar D?ffinger wrote:
> > > On Fri, Apr 17, 2009 at 10:05:27PM +0200, reimar wrote:
> > > > Author: reimar
> > > > Date: Fri Apr 17 22:05:27 2009
> > > > New Revision: 18599
> > > > 
> > > > Log:
> > > > Use sign_extend function instead of reimplementing it.
> > > > 
> > > > Modified:
> > > >    trunk/libavcodec/xan.c
> > > > 
> > > > Modified: trunk/libavcodec/xan.c
> > > > ==============================================================================
> > > > --- trunk/libavcodec/xan.c	Fri Apr 17 22:01:45 2009	(r18598)
> > > > +++ trunk/libavcodec/xan.c	Fri Apr 17 22:05:27 2009	(r18599)
> > > > @@ -333,16 +333,10 @@ static void xan_wc3_decode_frame(XanCont
> > > >              }
> > > >          } else {
> > > >              /* run-based motion compensation from last frame */
> > > > -            motion_x = *vector_segment >> 4;
> > > > -            motion_y = *vector_segment & 0xF;
> > > > +            motion_x = sign_extend(*vector_segment >> 4,  4);
> > > > +            motion_y = sign_extend(*vector_segment & 0xF, 4);
> > > 
> > > Someone forgot to document sign_extend, should I be doing the "& 0xF"
> > > or can I assume that any future optimized implementation will flush
> > > the upper bits, too?
> > 
> > the upper bits must be cleared
> 
> Do you mean "must have been cleared by the caller" or "must be cleared
> by the function"? This sounds like the latter, but
> 
> > its possible to implement sign extend with 1 + and 1 xor if the shift
> > is constant, and this may be faster than the 2 shifts ...
> 
> that would only work if you meant the former AFAICT.

i meant the former

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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