TalkChess.com

[Edsel Apostol]

Hi Les,

Maybe Rybka is using piece lists combined with bitboard. As what Bob has said, it is true that when you flip a position, the move ordering will also change, resulting to varying time to find the solution, that is if it is a bitboard only engine.

There is also a possibility that the eval value will change even if you have no bugs in your program. This results from the SEE routine, if it uses lastOne() only for both sides, applicable only for bitboards. (I'm using SEE in my eval ). Some positions have the same rooks for example to capture on a square, but when you flipped it the other rook will be tried first in the capture sequence that might result to a different value. It is also possible that in this kind of positions the SEE is inaccurate.

I even wrote a bitboard SEE that will overcome this issue but I'm wondering if the added accuracy can compensate for the little speed loss. This kind of positions are somewhat rare, maybe one in a hundred thousand positions in my guess. I have not tested that SEE much though and on my testing, there is no significant change that I noticed.

Edsel