[Gllug] Faster maths?

[salsaman]

Richard Jones wrote:

>On Thu, Mar 08, 2007 at 11:11:26PM +0000, Adrian McMenamin wrote:
>  
>
>>I have some perl which indexes and dithers a PNG image to a 256 colour
>>palette.
>>
>>The indexing is pretty fast - a 59K (compressed) PNG image on a 4000
>>BogoMIPS machine in about a second.
>>
>>But I turn on dithering it takes half an hour!!
>>
>>The bottleneck appears to be calculating the distance of a point in
>>colourspace (ie the original colour + diffused error) from any point in
>>the palette (to find the closest match).
>>
>>I don't use sqrt - just compare square with square (and save a match so
>>don't have to do the same lookup twice).
>>    
>>
>
>There's a fast, high-quality implementation of this algorithm in the
>source code to xv.  Unfortunately it has a non-free license ...
>
>Rich.
>
>  
>
Well, I already posted one algorithm you could use: 3d cube mapping. But 
if you want to  ignore that and calculate the inverse sqrt quickly, use 
the hack from ID software:

http://www.codemaestro.com/reviews/review00000105.html

Gabriel.

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