Author: Ed Schröder
Date: 13:52:14 01/07/03
Go up one level in this thread
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
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