Remove depth dependence in value_draw().

The condition "depth >= 4 * ONE_PLY" does not seem needed at this point.

passed STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 32751 W: 7178 L: 7078 D: 18495
http://tests.stockfishchess.org/tests/view/5d8e46660ebc590f3bebad5e

passed LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 31693 W: 5299 L: 5196 D: 21198
http://tests.stockfishchess.org/tests/view/5d8e4b4f0ebc590f3bebb165

Bench: 4062526

diff --git a/src/search.cpp b/src/search.cpp
index 01de12a4cea99b662ce0134349be1b3c3dadaeb5..2ad535ccb56b93ce1690eff7e9d800df1f077d23 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -86,9 +86,8 @@ namespace {
   }
 
   // Add a small random component to draw evaluations to avoid 3fold-blindness
-  Value value_draw(Depth depth, Thread* thisThread) {
-    return depth < 4 * ONE_PLY ? VALUE_DRAW
-                               : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
+  Value value_draw(Thread* thisThread) {
+    return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
   }
 
   // Skill structure is used to implement strength limit
@@ -574,7 +573,7 @@ namespace {
         && !rootNode
         && pos.has_game_cycle(ss->ply))
     {
-        alpha = value_draw(depth, pos.this_thread());
+        alpha = value_draw(pos.this_thread());
         if (alpha >= beta)
             return alpha;
     }
@@ -624,7 +623,7 @@ namespace {
             || pos.is_draw(ss->ply)
             || ss->ply >= MAX_PLY)
             return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
-                                                    : value_draw(depth, pos.this_thread());
+                                                    : value_draw(pos.this_thread());
 
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
         // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
@@ -763,7 +762,7 @@ namespace {
             ss->staticEval = eval = evaluate(pos);
 
         if (eval == VALUE_DRAW)
-            eval = value_draw(depth, thisThread);
+            eval = value_draw(thisThread);
 
         // Can ttValue be used as a better position evaluation?
         if (    ttValue != VALUE_NONE