[XviD-devel] basic gmc decoding

[Christoph Lampert]

On Mon, 4 Nov 2002, peter ross wrote:

> hi,
> 
> its done. whew, about 40 lines of code. (basic == one warp point)

Great! If it also handles two warp points when second point is (0,0) 
(as done by DivX5 and my XVID encoding) then it should be sufficient for
a while. 

> michaeln, ive borrowed your trajectory value code. for encoding,
> christoph has used a rather large lookup table, but your method is
> much more elegant.
> if ((x >> (length - 1)) == 0) /* if MSB not set it is negative*/
>      x = - (x ^ ((1 << length) - 1));

Yes, for decoding this is easy (because length is known). For encoding I
would have had to use a longer if-table to check for bounds of intervals
and I thought a table would be the easiest way. 

Maybe it can be done easier, I never tried to do VLC before. 

gruel 

P.S. Btw. there is are two lookup tables with 512K entries in vlc_codes.h 
Are those really used?