[XviD-devel] Decoder performance

[Christoph Lampert]

Hi Ed,

please be careful when replacing 

   if (quarterpel) 

by any arithmetic construction. From what I saw, quarterpel is not always
0 or 1, but 0 or "something", because e.g. MBMotionCompensation is called
with the value 

(current->vol_flags & XVID_VOL_QUARTERPEL)

For 'if's this is of course okay, for calculations like 
+(quarterpel&1)  etc. it's not! We would have to use some kind of 

(current->vol_flags & XVID_VOL_QUARTERPEL)?1:0 

or so... which is another 'if' in disguise, even thoughi it's evaluated
less often and also it might be assembled by a cmov or so. 

Christoph 



On Sat, 9 Aug 2003, Edouard Gomez wrote:
> Edouard Gomez (ed.gomez at free.fr) wrote:
> > #define div_2(a, b) (((a)-(((a)>>31)&(-b)))>>(b))
> 
> Don't know what happens to me, perhaps the heat... but the original code
> from gruel was right too :\ so forget these 2 last emails
> 
> -- 
> Edouard Gomez
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>