gnuchess bugs & java

[Xan Gregg]

I've been porting GNU Chess to Java, and it's working as far as I can  
tell. It's at least to the point where I can point out some of the  
bugs/suspicious code found in the C code.

1. In BookBuilderOpen(), there appears to be an unnecessary close()  
of rfp and later a read_book(wfp) which should probably be a read_book 
(rfp).

2. In ParseEPD(), there's a "if (!++p)" that should probably be a "if  
(!*++p)".

3. In ScoreK(), need to check that the king isn't on the last rank  
before checking for pawns in front of the king. Otherwise, who knows  
what you're looking at.

4. InitHashCode() should be called before InitVars(), because the  
latter makes use of the hashcodes.

5. Misplaced parenthesis in ValidateMove()?:

  if (piece_id(mvstr[2] != empty))

6. In IsLegalMove(), need to check that moving a pawn to the 8th rank  
is marked as a promotion. What happened while trying BT2630.epd was a  
move g2-g1 was cached as a killer when it was legal (maybe a rook on  
g2) and considered later when there was a pawn on g2. IsLegalMove()  
let it pass, which caused an array index out of bounds while later  
processing the position with a pawn on the 8th rank.

7. In PhasePick1(), there's a 'while' that could be an 'if': the body  
ends with a 'return'.

8. trailz() is a bit cryptic, but it looks like it returns the bit  
index of the trailing 1 but, not the number of trailing zeros as  
expected by the name.

9. About a dozen unused variables or values, if anyone cares.

That's about it. The Java 1.4.2 version is running about one half the  
speed of the C code on my Mac G5.

Question: It looks like the code is assuming that hash(position1) ==  
hash(position2) implies that position1 == position2. A hash has 64  
bits, but there are supposedly around 2^160 chess positions, so there  
must be about 2^96 positions for every hash code. Is the code relying  
on luck to avoid collisions, or is there something in the design that  
prevents them?

BTW, any way someone can get rid of all the spam on this list?

xan