Author: José Carlos
Date: 15:58:47 02/19/04
Go up one level in this thread
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)) Hi Tim. Your conversion is probably faster than mine. Here's the best I could figure out (in Averno): #define Trad0x88(x) ((((x)&120)<<1)|((x)&7)) // 64 -> 0x88 #define Trad64(x) (((x&240)>>1)|(x&7)) // 0x88 -> 64 I don't even remember how I came to them (trying out in paper, I think). I also recall I tried building a conversion array, but it turned out to be clearly slower. José C. >So you could then use... > >#define direction(i, j) (directionNumber[(TO88(i) - TO88(j)) & 0xFF]) > >Cheers, Tim.
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