Author: Ed Schröder
Date: 13:27:49 01/07/03
Go up one level in this thread
On January 07, 2003 at 14:57:22, Russell Reagan wrote: >+------+------+------+------+------+------+------+------+ >| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >+------+------+------+------+------+------+------+------+ >| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >| ATTACKERS | |BISHOP| | | | >+------+------+------+------+------+------+------+------+ > >Ed, > >On your webpage you have the above diagram. I am curious what you use bits 3-7 >for. The reason I ask is because what if there are two queens and one knight >attacking a square? Then the table will look like this: > >+------+------+------+------+------+------+------+------+ >| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >+------+------+------+------+------+------+------+------+ >| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >| ATTACKERS | |BISHOP| | | | >+------+------+------+------+------+------+------+------+ >| 1 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | >+------+------+------+------+------+------+------+------+ > >How do you know if there are two queens and one knight/bishop attacking, or two >knights/bishops and one queen? > >Let's look at an example: > >[D]4kq2/2bq2b1/8/4p3/4P3/2Q2N2/1Q2K1B1/8 w - - 0 1 > >In this position, the attack board for white[e5] is going to be: >+------+------+------+------+------+------+------+------+ >| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >+------+------+------+------+------+------+------+------+ >| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >| ATTACKERS | |BISHOP| | | | >+------+------+------+------+------+------+------+------+ >| 1 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | >+------+------+------+------+------+------+------+------+ > >In this other position: >[D]4kq2/2bq2b1/8/4p3/4P3/2B2N2/1Q2K1Q1/8 w - - 0 1 >The attack board for white[e5] is exactly the same as in the previous position, >but in this case, white can win the pawn, but in the first position white can >not win the pawn. > >When two attack boards are the same, as in these two positions, how do you >determine that the latter position is a gain of 1 pawn and the first position is >not? > >I understand how you compute the attack table, but I am a little confused about >how you use this information to arrive at a conclusion, like "white wins 1 >pawn". See my answer to Tony: http://www.talkchess.com/forums/1/message.html?275529 Also realize that the system isn't only to detect hanging pieces (move-ordering) or threats (forward pruning, reductions etc), it is also used for eval purposes. Ed >Thanks, >Russell
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