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Don't prune TT move in qsearch even if SEE < 0

Even if SEE is negative there is always a good possibility
that TT move is a cut move anyway. For instance a lot of
BXN exchanges that have negative SEE can very easily be
good exchanges.

A nice side effect is a bit reduced frequency of
see_sign() calls.

After 643 games at 1+0
Mod vs Orig +174 =327 -142 52.49%  337.5/643 +17 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
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1 parent cf4df03 commit a72c55283d132e64cad9101c65e59c1f9406be83 @mcostalba committed Oct 20, 2009
Showing with 2 additions and 1 deletion.
  1. +2 −1 src/search.cpp
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3 src/search.cpp
@@ -1596,6 +1596,7 @@ namespace {
// Don't search captures and checks with negative SEE values
if ( !isCheck
+ && move != ttMove
&& !move_is_promotion(move)
&& pos.see_sign(move) < 0)
continue;
@@ -1622,7 +1623,7 @@ namespace {
// All legal moves have been searched. A special case: If we're in check
// and no legal moves were found, it is checkmate.
- if (pos.is_check() && moveCount == 0) // Mate!
+ if (!moveCount && pos.is_check()) // Mate!
return value_mated_in(ply);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);

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