Author: Uri Blass
Date: 14:46:37 02/19/04
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On February 19, 2004 at 16:57:39, Tim Foden wrote: >On February 19, 2004 at 14:39:16, Uri Blass wrote: > >>Today I have an array direction[64][64] that gives me different numbers for >>different directions(possible directions are queen direction that get 0-7 knight >>directions that get -2,identical squares that get -9 or no direction that gets >>-1 ). >> >>I thought about the idea to change it to the following definition: >> >>#define direction((i)(j)) directionnumber[translate[i]-translate[j]+128] >> >>The result is that I can get instead of one array of 4096 entries >>2 arrays when translate is an array of 64 entries and directionnumber is an >>array of 256 entries. >> >>My question is if it is a good idea from speed point of view. >>It will probably be a simple change when I only need to construct the 2 arrays >>and the main problem is to construct the translate array. >> >>It is probably only few hours of work but I do not like to spend time on >>constructing these arrays only to discover later that it is not productive so I >>ask for your opinion about it. >> >>Uri > >If you converted the coordinates to 0x88 coordinates, you only need a 256 byte >lookup table. > >A macro to do the conversion from the 64 square system would be... > >#define TO88(sq) ((sq) + ((sq) & 0x38)) > >So you could then use... > >#define direction(i, j) (directionNumber[(TO88(i) - TO88(j)) & 0xFF]) > >Cheers, Tim. Thanks. I did not know that there is a macro for 0x88 coordinates and I only remembered that it allow you to know the direction based on difference. It seems faster than what I thought to do and the only question is if it is faster than what I have. Uri
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