Depth margin parameter-tweak in TT-save

Verified that is improvement with multiple threads:

LLR: 2.95 (-2.94,2.94) [0.00,4.00] sprt @ 30+0.3 th 3
Total: 14817 W: 2103 L: 1915 D: 10799

LLR: 2.96 (-2.94,2.94) [0.00,4.00] sprt @ 15+0.15 th 7
Total: 10264 W: 1498 L: 1321 D: 7445

Verified that is not a significant regression with a single thread:

LLR: 2.96 (-2.94,2.94) [-4.00,0.00] sprt @ 60+0.6 th 1
Total: 23975 W: 3294 L: 3210 D: 17471

Resolves #575

diff --git a/src/tt.h b/src/tt.h
index d411ffa867089da315be62167b7d0113bfc00a70..70283fca29bff341fd7d06d23ac12bacfdf8a66e 100644 (file)
--- a/src/tt.h
+++ b/src/tt.h
@@ -50,7 +50,7 @@ struct TTEntry {
 
     // Don't overwrite more valuable entries
     if (  (k >> 48) != key16
-        || d > depth8 - 2
+        || d > depth8 - 4
      /* || g != (genBound8 & 0xFC) // Matching non-zero keys are already refreshed by probe() */
         || b == BOUND_EXACT)
     {