Author: Anthony Cozzie
Date: 07:36:19 03/04/05
Go up one level in this thread
On March 04, 2005 at 09:51:14, Antonio Senatore wrote:
>Hi friends:
>
>I'm rewriting my engine so it can use bitboards now. However, something curious
>is happening. After having implemented with quite success the use of bitboards
>in others functions, now I'm trying to apply them in my evaluation function. As
>much as possible, I attempted to make the changes statement by statement to
>observe in what way the changes affected the speed of the engine. And here is
>where I am confused.
>
>So far, to determine if a passed pawn was or not sustained by its king, I used
>the following code (for a white pawn):
>
> if ((abs(column[wking_pos]-column[wpawn_pos]) <= 1) &&
>(abs(row[wking_pos]-row[wpawn_pos]) <= 1)) {
> ....
> etc.
> }
>
> where:
> 0 <= wking_pos <= 63 // 0 = A1, 1 = B1, etc.
> 0 <= wpawn_pos <= 63
>
>
>I changed that code for the following:
>
> if (king_attack[wpawn_pos] & WhiteKing) {
> ....
> etc.
> }
>
>For my surprise, the code that uses bitboards is slower than the first one
>(according to some own bench tests), not much, but slower after all. How can it
>be possible? Because in the first case I make two comparisons and use the abs()
>function twice meanwhile in the second case I only make a bitwise-AND operation
>(of course, with 64 bit numbers in a 32 bit system, but even so, I think it
>should be faster) Can anyone tell me what I'm doing bad? Additionally, the same
>thing happens to me with:
>
>If (!(king_attack[wking_pos] & WhitePieces)) {
> ....
> etc.
>}
>
>that I attempted to use to see if the white king is or not surrounded for, at
>least, one own piece. Surprisingly, the code that makes the same thing by
>checking square by square (on the eight squares that surround the king) is a bit
>faster. I work with MSVC++ 6.0
>
>Many thanks in advance for any comentary that you can do.
>
>Regards
>Antonio
Bitboards just aren't faster. IMO on 32-bits they are slower; on 64-bits they
are break even. I still use them though, simply because I've gotten to the
point where I think in them more easily then I think in board[64]. Your
particular example involves what is probably an L2 load: 13 cycles to get the
mask value.
anthony
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