More precise checks evaluation in king danger

Remove overlapping safe checks from kingdanger:
- rook and queen checks from the same square: rook check is preferred
- bishop and queen checks form the same square: queen check is preferred

Increase bishop and rook check values as a compensation.

STC
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 27480 W: 6111 L: 5813 D: 15556
http://tests.stockfishchess.org/tests/view/5c521d050ebc593af5d4e66a

LTC
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 78500 W: 13145 L: 12752 D: 52603
http://tests.stockfishchess.org/tests/view/5c52b9460ebc592fc7baecc5

Closes https://github.com/official-stockfish/Stockfish/pull/1983

------------------------------------------

I have quite a few ideas of how to improve this patch.

- actually rethinking it now it will maybe be useful to discount
  queen/bishop checks if there is only one square that they can
  give check from and it's "occupied" by more valuable check. Right
  now count of this squares does not really matter.

- maybe some small extra bonus can be given for overlapping checks.

- some ideas about using popcount() on safechecks can be retried.

- tune this safecheck values since they were more or less randomly handcrafted in this patch.

Bench: 3216489

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 6bacb4eddb533f8a4f76189b136e48e641d4aae1..da90eed974e81a4c80780fc4bb953432cee20914 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -93,8 +93,8 @@ namespace {
 
   // Penalties for enemy's safe checks
   constexpr int QueenSafeCheck  = 780;
-  constexpr int RookSafeCheck   = 880;
-  constexpr int BishopSafeCheck = 435;
+  constexpr int RookSafeCheck   = 1080;
+  constexpr int BishopSafeCheck = 635;
   constexpr int KnightSafeCheck = 790;
 
 #define S(mg, eg) make_score(mg, eg)
@@ -434,27 +434,42 @@ namespace {
     b1 = attacks_bb<ROOK  >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
     b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
 
-    // Enemy queen safe checks
-    if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
-        kingDanger += QueenSafeCheck;
-
-    b1 &= attackedBy[Them][ROOK];
-    b2 &= attackedBy[Them][BISHOP];
-
     // Enemy rooks checks
-    if (b1 & safe)
+    Bitboard RookCheck =  b1
+                        & safe
+                        & attackedBy[Them][ROOK];
+
+    if (RookCheck)
         kingDanger += RookSafeCheck;
     else
-        unsafeChecks |= b1;
+        unsafeChecks |= b1 & attackedBy[Them][ROOK];
+
+    // Enemy queen safe checks: we count them only if they are from squares from
+    // which we can't give a rook check, because rook checks are more valuable.
+    Bitboard QueenCheck =  (b1 | b2)
+                         & attackedBy[Them][QUEEN]
+                         & safe
+                         & ~attackedBy[Us][QUEEN]
+                         & ~RookCheck;
 
-    // Enemy bishops checks
-    if (b2 & safe)
+    if (QueenCheck)
+        kingDanger += QueenSafeCheck;
+
+    // Enemy bishops checks: we count them only if they are from squares from
+    // which we can't give a queen check, because queen checks are more valuable.
+    Bitboard BishopCheck =  b2 
+                          & attackedBy[Them][BISHOP]
+                          & safe
+                          & ~QueenCheck;
+
+    if (BishopCheck)
         kingDanger += BishopSafeCheck;
     else
-        unsafeChecks |= b2;
+        unsafeChecks |= b2 & attackedBy[Them][BISHOP];
 
     // Enemy knights checks
     b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
+
     if (b & safe)
         kingDanger += KnightSafeCheck;
     else