Remove pawn count in space() calculation #2139

Simplification. Various attempts to optimise the pawn
count bonus showed little effect, so remove pawn count
altogether and compensate by subtracting 1 instead of 4.

STC 10+0.1 th 1:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 152244 W: 33709 L: 33847 D: 84688
http://tests.stockfishchess.org/tests/view/5cceed330ebc5925cf04170e

LTC 60+0.6 th 1:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 24100 W: 4079 L: 3964 D: 16057
http://tests.stockfishchess.org/tests/view/5cd5b6b80ebc5925cf04e889

Bench: 3648841

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 5750d82a7281bbd9ff91f6b22f137b9e9fac0600..d1a8ffd31fb4ab954ed3849bfa927d58bde5c3bf 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -719,9 +719,7 @@ namespace {
     behind |= shift<Down+Down>(behind);
 
     int bonus = popcount(safe) + popcount(behind & safe);
     behind |= shift<Down+Down>(behind);
 
     int bonus = popcount(safe) + popcount(behind & safe);

-    int weight =  pos.count<ALL_PIECES>(Us)
-               - (16 - pos.count<PAWN>()) / 4;
-
+    int weight = pos.count<ALL_PIECES>(Us) - 1;

     Score score = make_score(bonus * weight * weight / 16, 0);
 
     if (T)
     Score score = make_score(bonus * weight * weight / 16, 0);
 
     if (T)