Author: Ricardo Gibert
Date: 19:29:01 06/25/02
Go up one level in this thread
On June 25, 2002 at 22:20:32, Miguel A. Ballicora wrote:
>On June 24, 2002 at 22:19:53, Filip Tvrzsky wrote:
>
>>On June 24, 2002 at 20:33:32, Russell Reagan wrote:
>>
>>>I am not an experienced bitboard user. I've been thinking about trying them out
>>>just to see how they work in comparison with my current 0x88 implementation. Is
>>>there any potential problem in mixing the two approaches? One problem that I can
>>>see would be that if you have an index for a bitboard, it's not going to index
>>>into the same square in your 0x88 array. I suppose the only real reason to keep
>>>0x88 would be for efficient edge detection. Do bitboards offer a solution to
>>>edge detection? Or do they even need edge detection when using bitboards (ex.
>>>using the BSF asm instuction would seem to avoid edge detection altogheter)?
>>>
>>>Thanks,
>>>Russell
>>
>>I am not an experienced bitboard user too ... :-), but I have tried to mix both
>>approaches in my program, so I think it is possible very well. I assume x86 CPU
>>architecture farther, because I have no another expierence. My goal was to take
>>advantage of bitboards anywhere if it could be more efficient then pure 0x88
>>representation, so I choose the way of improvement of my originally 0x88 program
>>step by step. It is simple with knights and pawns, somewhat more complicated
>>with rooks and most of all with bishops (I do not use bitboards here yet, but I
>>work on it now). Something is possible to do with MMX instructions, but this
>>instruction set has unfortunately many limitations. Generally I use bitboards by
>>move generator, check detector and in evaluation function too. The cost of
>>simultaneous keeping both 0x88 and bitboard representations is, in my opinion,
>>more then outweighted by gains. The pure bitboard representation seems to me to
>>be rather unefficient on x86 architecture, but I am not sure, I do not know it
>>in detail.
>>And regarding indexes for bitboards and 0x88 board, the mapping of one on other
>>is not complicated, just 3 or 4 CPU instructions, no memory acces is needed:
>>
>>A - bitboard index (range 0-63),
>>B - 0x88 index (range 0-7, 16-24, ... 112-119).
>>
>>Now, A == (B + (B & 7)) >> 1, and B == A + (A & ~7)
>
>These calculations do not look right...
>
>Aren't they suppose to be like this?
Don't ask. Think!
>
>unsigned int sq_to_x88 (unsigned int s)
>{
> return ((s & 070) << 1) | (s & 07);
>}
>
>unsigned int x88_to_sq (unsigned int x)
>{
> return ((x & 0x70) >> 1) | (x & 07);
>}
>
>
>Miguel
>
>
>
>>
>>Greeting you, Filip.
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