Smart TT save

Don't overwrite more valuable data with less valuable data

STC 2MB
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 21132 W: 4108 L: 3946 D: 13078
http://tests.stockfishchess.org/tests/view/5547d59f0ebc5940ca5d6883

LTC 8MB
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 13381 W: 2149 L: 1987 D: 9245
http://tests.stockfishchess.org/tests/view/5549b5a80ebc5940ca5d68b9

STC 16MB regression w/ zero effective hash pressure
LLR: 2.96 (-2.94,2.94) [-5.00,0.00]
Total: 18944 W: 3607 L: 3564 D: 11773
http://tests.stockfishchess.org/tests/view/554b0fda0ebc5940ca5d68ea

Bench: 8787152

Resolves #347

diff --git a/src/tt.h b/src/tt.h
index 32b4036e39dea085974410867b7212facfc6c625..48c5638a7d971d1ed3c581a37b7a87529948d462 100644 (file)
--- a/src/tt.h
+++ b/src/tt.h
@@ -43,14 +43,34 @@ struct TTEntry {
 
   void save(Key k, Value v, Bound b, Depth d, Move m, Value ev, uint8_t g) {
 
-    if (m || (k >> 48) != key16) // Preserve any existing move for the same position
-        move16 = (uint16_t)m;
-
-    key16     = (uint16_t)(k >> 48);
-    value16   = (int16_t)v;
-    eval16    = (int16_t)ev;
-    genBound8 = (uint8_t)(g | b);
-    depth8    = (int8_t)d;
+      if (key16 != (k >> 48))
+      {
+          key16     = (uint16_t)(k >> 48);
+          move16    = (uint16_t)m;
+          value16   = (int16_t)v;
+          eval16    = (int16_t)ev;
+          genBound8 = (uint8_t)(g | b);
+          depth8    = (int8_t)d;
+      }
+      else
+      {
+          // Preserve any existing move for the same position
+          if (m)
+              move16 = (uint16_t)m;
+
+          // Don't overwrite more valuable values
+          if (   d + 2 > depth8 
+              || g != (genBound8 & 0xFC) 
+              || b == BOUND_EXACT)
+          {
+              value16   = (int16_t)v;
+              genBound8 = (uint8_t)(g | b);
+              depth8    = (int8_t)d;
+          }
+
+          if (ev != VALUE_NONE)
+              eval16 = (int16_t)ev;
+      }
   }
 
 private: