Simplify other checks #1334

Simplify the other check penalty computation. Compared to current master,

a) it uses a 143 kingDanger penalty instead of S(10, 10) for the "otherCheck"
(credits to ElbertoOne for finding a suitable kingDanger range to replace the score
and to Guardian for showing this could also be a neutral change at LTC).
This makes our king safety model more consistent and simpler.

b) it might also score more than one "otherCheck" penalty for a given piece type instead of just one

c) it might score many pinned penalties instead of just one.

d) It also remove 3 conditionals and uses simpler expressions.
So it was tested as a SPRT[-3, 1]

Passed STC
http://tests.stockfishchess.org/tests/view/5a2b560b0ebc590ccbb8ba6b
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 11705 W: 2217 L: 2080 D: 7408

And LTC
http://tests.stockfishchess.org/tests/view/5a2bfd0d0ebc590ccbb8bab0
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 26812 W: 3575 L: 3463 D: 19774

Trying to improve on b) another attempt was made to score also the
"otherchecks" for piece types which had some safe checks, but this
failed STC http://tests.stockfishchess.org/tests/view/5a2c79e60ebc590ccbb8badd

bench: 5149133

src/evaluate.cpp

@@ -111,7 +111,8 @@ namespace {
     Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
 
     // attackedBy[color][piece type] is a bitboard representing all squares
-    // attacked by a given color and piece type (can be also ALL_PIECES).
+    // attacked by a given color and piece type. Special "piece types" which are
+    // also calculated are QUEEN_DIAGONAL and ALL_PIECES.
     Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
 
     // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
@@ -217,7 +218,6 @@ namespace {
   const Score RookOnPawn            = S(  8, 24);
   const Score TrappedRook           = S( 92,  0);
   const Score WeakQueen             = S( 50, 10);
-  const Score OtherCheck            = S( 10, 10);
   const Score CloseEnemies          = S(  7,  0);
   const Score PawnlessFlank         = S( 20, 80);
   const Score ThreatByHangingPawn   = S( 71, 61);
@@ -237,10 +237,10 @@ namespace {
   const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
 
   // Penalties for enemy's safe checks
-  const int QueenCheck  = 780;
+  const int QueenSafeCheck  = 780;
-  const int RookCheck   = 880;
+  const int RookSafeCheck   = 880;
-  const int BishopCheck = 435;
+  const int BishopSafeCheck = 435;
-  const int KnightCheck = 790;
+  const int KnightSafeCheck = 790;
 
   // Threshold for lazy and space evaluation
   const Value LazyThreshold  = Value(1500);
@@ -428,7 +428,7 @@ namespace {
                                         : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
 
     const Square ksq = pos.square<KING>(Us);
-    Bitboard weak, b, b1, b2, safe, other;
+    Bitboard weak, b, b1, b2, safe, unsafeChecks;
     int kingDanger;
 
     // King shelter and enemy pawns storm
@@ -442,18 +442,7 @@ namespace {
               & ~attackedBy2[Us]
               & (attackedBy[Us][KING] | attackedBy[Us][QUEEN] | ~attackedBy[Us][ALL_PIECES]);
 
-        // Initialize the 'kingDanger' variable, which will be transformed
+        kingDanger = unsafeChecks = 0;
-        // later into a king danger score. The initial value is based on the
-        // number and types of the enemy's attacking pieces, the number of
-        // attacked and weak squares around our king, the absence of queen and
-        // the quality of the pawn shelter (current 'score' value).
-        kingDanger =        kingAttackersCount[Them] * kingAttackersWeight[Them]
-                    + 102 * kingAdjacentZoneAttacksCount[Them]
-                    + 191 * popcount(kingRing[Us] & weak)
-                    + 143 * bool(pos.pinned_pieces(Us))
-                    - 848 * !pos.count<QUEEN>(Them)
-                    -   9 * mg_value(score) / 8
-                    +  40;
 
         // Analyse the safe enemy's checks which are possible on next move
         safe  = ~pos.pieces(Them);
@@ -464,35 +453,42 @@ namespace {
 
         // Enemy queen safe checks
         if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
-            kingDanger += QueenCheck;
+            kingDanger += QueenSafeCheck;
 
-        // Some other potential checks are also analysed, even from squares
+        b1 &= attackedBy[Them][ROOK];
-        // currently occupied by the opponent own pieces, as long as the square
+        b2 &= attackedBy[Them][BISHOP];
-        // is not attacked by our pawns, and is not occupied by a blocked pawn.
-        other = ~(   attackedBy[Us][PAWN]
-                  | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
 
-        // Enemy rooks safe and other checks
+        // Enemy rooks checks
-        if (b1 & attackedBy[Them][ROOK] & safe)
+        if (b1 & safe)
-            kingDanger += RookCheck;
+            kingDanger += RookSafeCheck;
+        else
+            unsafeChecks |= b1;
 
-        else if (b1 & attackedBy[Them][ROOK] & other)
+        // Enemy bishops checks
-            score -= OtherCheck;
+        if (b2 & safe)
+            kingDanger += BishopSafeCheck;
+        else
+            unsafeChecks |= b2;
 
-        // Enemy bishops safe and other checks
+        // Enemy knights checks
-        if (b2 & attackedBy[Them][BISHOP] & safe)
-            kingDanger += BishopCheck;
-
-        else if (b2 & attackedBy[Them][BISHOP] & other)
-            score -= OtherCheck;
-
-        // Enemy knights safe and other checks
         b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
         if (b & safe)
-            kingDanger += KnightCheck;
+            kingDanger += KnightSafeCheck;
+        else
+            unsafeChecks |= b;
 
-        else if (b & other)
+        // Unsafe or occupied checking squares will also be considered, as long as
-            score -= OtherCheck;
+        // the square is not defended by our pawns or occupied by a blocked pawn.
+        unsafeChecks &= ~(   attackedBy[Us][PAWN]
+                          | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
+
+        kingDanger +=        kingAttackersCount[Them] * kingAttackersWeight[Them]
+                     + 102 * kingAdjacentZoneAttacksCount[Them]
+                     + 191 * popcount(kingRing[Us] & weak)
+                     + 143 * popcount(pos.pinned_pieces(Us) | unsafeChecks)
+                     - 848 * !pos.count<QUEEN>(Them)
+                     -   9 * mg_value(score) / 8
+                     +  40;
 
         // Transform the kingDanger units into a Score, and substract it from the evaluation
         if (kingDanger > 0)