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Fix critical SEE bug

Browse source 
It is somewhat unbilievable but our SEE is broken !

If the first SEE move is a king capture and square is
defended then SEE continues instead of breaking.

The bug shows only on normal SEE, not see_sign() so
probing with a:

dbg_hit_on_c(slIndex==1, captured == KING);

reports just a tiny:

Total 3465656 Hits 6646 hit rate (%) 0

Bug was there since 351ef5c85b of 26/6/2011 (!)
although for some reason didn't show immediately, indeed the
bougous patch was a "No functional change" (!!)

bench: 4793754
This commit is contained in:
Marco Costalba 2013-07-20 13:03:45 +02:00
parent 0504a6975d
commit a6c5b4c6fb
1 changed files with 7 additions and 10 deletions
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17
src/position.cpp
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@ -1136,7 +1136,7 @@ int Position::see_sign(Move m) const {
// Early return if SEE cannot be negative because captured piece value
// is not less then capturing one. Note that king moves always return
// here because king midgame value is set to 0.
if (PieceValue[MG][piece_on(to_sq(m))] >= PieceValue[MG][piece_moved(m)])
if (PieceValue[MG][piece_moved(m)] <= PieceValue[MG][piece_on(to_sq(m))])
return 1;
return see(m);
@ -1197,6 +1197,12 @@ int Position::see(Move m, int asymmThreshold) const {
do {
assert(slIndex < 32);
if (captured == KING) // Stop before processing a king capture
{
swapList[slIndex++] = QueenValueMg * 16;
break;
}
// Add the new entry to the swap list
swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
slIndex++;
@ -1206,15 +1212,6 @@ int Position::see(Move m, int asymmThreshold) const {
stm = ~stm;
stmAttackers = attackers & pieces(stm);
if (captured == KING)
{
// Stop before processing a king capture
if (stmAttackers)
swapList[slIndex++] = QueenValueMg * 16;
break;
}
} while (stmAttackers);
// If we are doing asymmetric SEE evaluation and the same side does the first