Extend all moves at low depth if ttMove is doubly extended

If ttMove is doubly extended, we allow a depth growth of the remaining moves.
The idea is to get a more realistic score comparison, because of the depth
difference. We take some care to avoid this extension for high depths,
in order to avoid the cost, since the search result is supposed
to be more accurate in this case.

This pull request includes some small cleanups.

STC:
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 60256 W: 16189 L: 15848 D: 28219
Ptnml(0-2): 182, 6546, 16330, 6889, 181
https://tests.stockfishchess.org/tests/view/639109a1792a529ae8f27777

LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 106232 W: 28487 L: 28053 D: 49692
Ptnml(0-2): 46, 10224, 32145, 10652, 49
https://tests.stockfishchess.org/tests/view/63914cba792a529ae8f282ee

closes https://github.com/official-stockfish/Stockfish/pull/4271

Bench: 3622368

diff --git a/src/search.cpp b/src/search.cpp
index 04f73e1c0a28da06dd764352656a6725386524d3..ec7cff5413e8ae2935f3b3a2775b0e5e3114fb5d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1067,7 +1067,10 @@ moves_loop: // When in check, search starts here
                   if (  !PvNode
                       && value < singularBeta - 25
                       && ss->doubleExtensions <= 9)
+                  {
                       extension = 2;
+                      depth += depth < 12;
+                  }
               }
 
               // Multi-cut pruning
@@ -1296,7 +1299,7 @@ moves_loop: // When in check, search starts here
                       && depth < 6
                       && beta  <  VALUE_KNOWN_WIN
                       && alpha > -VALUE_KNOWN_WIN)
-                     depth -= 1;
+                      depth -= 1;
 
                   assert(depth > 0);
               }
@@ -1521,7 +1524,6 @@ moves_loop: // When in check, search starts here
           &&  futilityBase > -VALUE_KNOWN_WIN
           &&  type_of(move) != PROMOTION)
       {
-
           if (moveCount > 2)
               continue;
 

diff --git a/src/types.h b/src/types.h
index c2087c6c07b9e8fd84be7d3033c19da397f894b7..29c16ce7dbb8f877127f16e00cff5d618540fb56 100644 (file)
--- a/src/types.h
+++ b/src/types.h
@@ -186,6 +186,9 @@ enum Value : int {
   VALUE_MATE_IN_MAX_PLY  =  VALUE_MATE - MAX_PLY,
   VALUE_MATED_IN_MAX_PLY = -VALUE_MATE_IN_MAX_PLY,
 
+  // In the code, we make the assumption that these values
+  // are such that non_pawn_material() can be used to uniquely
+  // identify the material on the board.
   PawnValueMg   = 126,   PawnValueEg   = 208,
   KnightValueMg = 781,   KnightValueEg = 854,
   BishopValueMg = 825,   BishopValueEg = 915,