Don't fear races when are harmless

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 056dc250377a9ecf8ae63ab3270247f3cc331da3..6d900f7bb7ae673575f2d52b953ed63ca2c2d3ff 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -595,7 +595,7 @@ namespace {
     // Step 6. Razoring (skipped when in check)
     if (   !PvNode
         &&  depth < 4 * ONE_PLY
-        &&  eval + razor_margin(depth) < beta
+        &&  eval + razor_margin(depth) <= alpha
         &&  ttMove == MOVE_NONE
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
         && !pos.pawn_on_7th(pos.side_to_move()))
@@ -635,29 +635,13 @@ namespace {
 
         pos.do_null_move(st);
         (ss+1)->skipNullMove = true;
-        nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
-                                      : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
+        nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
+                                      : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
         (ss+1)->skipNullMove = false;
         pos.undo_null_move();
 
-        if (nullValue >= beta)
-        {
-            // Do not return unproven mate scores
-            if (nullValue >= VALUE_MATE_IN_MAX_PLY)
-                nullValue = beta;
-
-            if (depth < 12 * ONE_PLY)
-                return nullValue;
-
-            // Do verification search at high depths
-            ss->skipNullMove = true;
-            Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO)
-                                        :  search<NonPV>(pos, ss, alpha, beta, depth-R, false);
-            ss->skipNullMove = false;
-
-            if (v >= beta)
-                return nullValue;
-        }
+        if (nullValue >= beta) // Do not return unproven mate scores
+            return nullValue >= VALUE_MATE_IN_MAX_PLY ? beta : nullValue;
     }
 
     // Step 9. ProbCut (skipped when in check)