Simplify away non-normal moves in SEE

credit goes to @mstembera for suggesting this approach.
SEE now deals with castling, promotion and en passant in a similar way.

passed STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 32902 W: 6079 L: 5979 D: 20844

passed LTC
LLR: 3.92 (-2.94,2.94) [-3.00,1.00]
Total: 110698 W: 14198 L: 14145 D: 82355

Bench: 5713905

diff --git a/src/position.cpp b/src/position.cpp
index 49935904bdc5b03afa2418bd342140a000861fe6..bda83d7a138f8a6dc8c80b7b99a8bb75382e9d36 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -993,10 +993,8 @@ bool Position::see_ge(Move m, Value threshold) const {
 
   assert(is_ok(m));
 
-  // Castling moves are implemented as king capturing the rook so cannot be
-  // handled correctly. Simply assume the SEE value is VALUE_ZERO that is always
-  // correct unless in the rare case the rook ends up under attack.
-  if (type_of(m) == CASTLING)
+  // Only deal with normal moves, assume others pass a simple see
+  if (type_of(m) != NORMAL)
       return VALUE_ZERO >= threshold;
 
   Square from = from_sq(m), to = to_sq(m);
@@ -1005,16 +1003,8 @@ bool Position::see_ge(Move m, Value threshold) const {
   Value balance; // Values of the pieces taken by us minus opponent's ones
   Bitboard occupied, stmAttackers;
 
-  if (type_of(m) == ENPASSANT)
-  {
-      occupied = SquareBB[to - pawn_push(~stm)]; // Remove the captured pawn
-      balance = PieceValue[MG][PAWN];
-  }
-  else
-  {
-      balance = PieceValue[MG][piece_on(to)];
-      occupied = 0;
-  }
+  balance = PieceValue[MG][piece_on(to)];
+  occupied = 0;
 
   if (balance < threshold)
       return false;