small cleanups

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index c042c016ed35c511b304938332b918da188e96d7..3b0891a2d4fbfc1af9c10b8b84ea04309746c9fe 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -676,16 +676,15 @@ namespace {
   }
 
 
-  // Evaluation::space() computes the space evaluation for a given side. The
-  // space evaluation is a simple bonus based on the number of safe squares
-  // available for minor pieces on the central four files on ranks 2--4. Safe
-  // squares one, two or three squares behind a friendly pawn are counted
-  // twice. Finally, the space bonus is multiplied by a weight. The aim is to
-  // improve play on game opening.
+  // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
+  // play in the opening. It is based on the number of safe squares on the 4 central files
+  // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
+  // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
 
   template<Tracing T> template<Color Us>
   Score Evaluation<T>::space() const {
 
+    // Early exit if, for example, both queens or 6 minor pieces have been exchanged
     if (pos.non_pawn_material() < SpaceThreshold)
         return SCORE_ZERO;
 
@@ -743,7 +742,6 @@ namespace {
                     + 24 * infiltration
                     + 51 * !pos.non_pawn_material()
                     - 43 * almostUnwinnable
-                    -  2 * pos.rule50_count()
                     -110 ;
 
     Value mg = mg_value(score);
@@ -856,8 +854,16 @@ namespace {
         Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
     }
 
+    // Evaluation grain
+    v = (v / 16) * 16;
+
     // Side to move point of view
-    return (pos.side_to_move() == WHITE ? v : -v) + Tempo;
+    v = (pos.side_to_move() == WHITE ? v : -v) + Tempo;
+
+    // Damp down the evaluation linearly when shuffling
+    v = v * (100 - pos.rule50_count()) / 100;
+
+    return v;
   }
 
 } // namespace