Reintroduce rook contact checks

Were removed when merged from Glaurung 2.2, but without
any test.

Note that weight has been increased from original 2 to 4 and
has been also fixed a bug where in the original version were
considered also diagonal sqaures for the rook, that are
contact squares but not checks.

After 4449 games at 30"+0.1
Mod - Orig:  717 - 649 - 3083  ELO +5 (+- 4.1)

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 1c215dc0d4a19b586189676331751e7e43845c9b..db08b1c49e22179fee74b556741104ec3c5d1567 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -200,6 +200,7 @@ namespace {
 
   // Bonuses for enemy's safe checks
   const int QueenContactCheckBonus = 6;
+  const int RookContactCheckBonus  = 4;
   const int QueenCheckBonus        = 3;
   const int RookCheckBonus         = 2;
   const int BishopCheckBonus       = 1;
@@ -710,6 +711,24 @@ namespace {
                               * (Them == pos.side_to_move() ? 2 : 1);
         }
 
+        // Analyse enemy's safe rook contact checks. First find undefended
+        // squares around the king attacked by enemy rooks...
+        b = undefended & ei.attackedBy[Them][ROOK] & ~pos.pieces_of_color(Them);
+
+        // Consider only squares where the enemy rook gives check
+        b &= RookPseudoAttacks[ksq];
+
+        if (b)
+        {
+            // ...then remove squares not supported by another enemy piece
+            b &= (  ei.attackedBy[Them][PAWN]   | ei.attackedBy[Them][KNIGHT]
+                  | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][QUEEN]);
+            if (b)
+                attackUnits +=  RookContactCheckBonus
+                              * count_1s_max_15<HasPopCnt>(b)
+                              * (Them == pos.side_to_move() ? 2 : 1);
+        }
+
         // Analyse enemy's safe distance checks for sliders and knights
         safe = ~(pos.pieces_of_color(Them) | ei.attackedBy[Us][0]);