# Computer Chess Club Archives

## Messages

### Subject: Re: hanging pieces in rebel

Author: Robert Hyatt

Date: 07:02:39 01/16/04

Go up one level in this thread

```On January 15, 2004 at 14:49:21, Bernward Klocke wrote:

>I recently read Ed Schroeder's comments on move ordering in rebel. What I find
>puzzeling is the way it detects hanging pieces.
>Ed presents the following data structure for square evaluation:
>+------+------+------+------+------+------+------+------+
>| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 |
>+------+------+------+------+------+------+------+------+
>|      Number of     | PAWN |KNIGHT| ROOK | QUEEN| KING |
>|      ATTACKERS     |      |BISHOP|      |      |      |
>+------+------+------+------+------+------+------+------+
>
>After all white pieces are done square F3 from WB looks as follows:
>+------+------+------+------+------+------+------+------+  B0-B2 : 2 attackers
>| BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 |
>+------+------+------+------+------+------+------+------+  B3    : white pawn
>|      Number of     | PAWN |KNIGHT| ROOK | QUEEN| KING |
>|      ATTACKERS     |      |BISHOP|      |      |      |  B4    : white
>knight/bishop
>+------+------+------+------+------+------+------+------+
>|  0   |   1  |  0   |  1   |  1   |  0   |  0   |  0   |
>+------+------+------+------+------+------+------+------+
>So evaluation is done for each square for black and for white. His example show
>the square f3 for white attacked by a pawn from f3 and a knight from g1.
>This example is clear but I think gets ambiguous when three pieces attack a
>square and two of them are of the same type eg. two rooks and a knight. How can
>one see that it's not two knights and one rook.
>And the other thing is only going through the movelist isn't the whole story.
>What if doubled rooks are the attackers? Only the first one will appear in the
>movelist.
>Does anybody know how this is solved. What did I miss?
>Otherwise the lookup from a precalculated table of STATUS values seems elegant.
>
>Bernward

I would worry about overflow there.

IE e4 could be attacked by pawns on d3 and f3, a bishop at d5 with a queen
behind it (4 so far), plus two rooks and two knights.  That's 8.  It just
overflowed to zero.  Not to mention the promotion problems where there is a
third knight or bishop or second queen...

```

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