Author: Antonio Senatore
Date: 06:51:14 03/04/05
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
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