Author: Uri Blass
Date: 01:31:23 01/08/03
Go up one level in this thread
On January 07, 2003 at 16:52:14, Ed Schröder wrote: >On January 07, 2003 at 16:05:06, Tord Romstad wrote: > >>On January 07, 2003 at 07:17:27, Ed Schröder wrote: >>> >>>Let's go through a couple of xray examples: >>> >>>[d]rn1qkbnr/pbppp1pp/1p3p2/8/2B5/1QP1P3/PP1P1PPP/RNB1K1NR b KQkq - >>> >>>The knight on G8 is hanging, 2 attackers, one defender, the lowest attacking >>>piece is a bishop. You can extract this from the bit settings. >>> >>> >>> >>> >>> >>> >>> >>>[d]r2qkbnr/pbppp1pp/1pn2p2/3Q4/2B5/2P1P3/PP1P1PPP/RNB1K1NR b KQkq - >>> >>>The knight on G8 is not hanging because the lowest attacking piece is a Queen. >> >>I still don't quite understand this, I'm afraid. How do you determine the >>lowest attacking piece from your bit settings in the presence of an x-ray >>attack? How do WB[G8] look for the above two positions? The way I understand >>the section about Rebel's eval on your homepage, the bit vector would look like >>this in both cases: >> >>+------+------+------+------+------+------+------+------+ >>| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >>+------+------+------+------+------+------+------+------+ >>| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >>| ATTACKERS | |BISHOP| | | | >>+------+------+------+------+------+------+------+------+ >>| 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | >>+------+------+------+------+------+------+------+------+ >> >>Clearly I am misunderstanding something, but I am not sure what ... >> >>Tord > > >I had to look at the code to understand myself, it's stuff from 16-18 years >back. > >We are scanning Bc4: > >Bc4 -> Qd5 -> e6 -> f7 -> Ng8 > >The squares AFTER d5 (e6, f7 and g8) the bits are not set, only a WB[sqaure]++; >is done, so the square G8 will look as follows: > >>+------+------+------+------+------+------+------+------+ >>| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | >>+------+------+------+------+------+------+------+------+ >>| Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | >>| ATTACKERS | |BISHOP| | | | >>+------+------+------+------+------+------+------+------+ >>| 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | >>+------+------+------+------+------+------+------+------+ > ^^^^^^^^ > >Hope this helps :) > >Ed take the following position [D]4n1k1/8/5b2/8/5R2/5R2/8/6K1 w - - 0 1 I guess that you have the following bits for white about f6 +------+------+------+------+------+------+------+------+ | BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | +------+------+------+------+------+------+------+------+ | Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | | ATTACKERS | |BISHOP| | | | +------+------+------+------+------+------+------+------+ | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | +------+------+------+------+------+------+------+------+ the following bits are for black +------+------+------+------+------+------+------+------+ | BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 | +------+------+------+------+------+------+------+------+ | Number of | PAWN |KNIGHT| ROOK | QUEEN| KING | | ATTACKERS | |BISHOP| | | | +------+------+------+------+------+------+------+------+ | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | +------+------+------+------+------+------+------+------+ I guess that in this case your table tell you that the bishop at f6 is hanging but the value of hang is only 1 because if you have rook and 2 attackers and knight bishop as single defender it means that knight is hanging by 1 pawn. Am I correct? Note that The main problem that I find when I think about it is not wrong detection of hanging pieces when there are 2 defenders and 3 attackers but wrong detection when there are pins(not to the king assuming that you have a legal move generator) or other threats. Consider the following position [D]rn1qkbnr/ppp2ppp/8/3pp3/4P1b1/3P1N2/PPP2PPP/RNBQKB1R w KQkq - 0 1 I guess that Rebel will detext the pawn at e5 as hanged. consider the following position [D]5bk1/8/8/2R5/8/R7/8/6K1 w - - 0 1 The a3 rook is also under indirect threat so it may be better to consider it for better order of moves Uri
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