Remove PvNode template from reduction

This functional simplification removes the PvNode reduction and adjusts
the ttPv lmr condition accordingly. Their definitions only differ by the
inclusions of ttPv. Aside from this, shallow move pruning definition
will be the only other functional difference, but this does not seem to
matter too much.

STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 58908 W: 12980 L: 12932 D: 32996
http://tests.stockfishchess.org/tests/view/5cd1aaaa0ebc5925cf046c6a

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 20351 W: 3521 L: 3399 D: 13431
http://tests.stockfishchess.org/tests/view/5cd23fa70ebc5925cf047cd2

Bench: 3687854

diff --git a/src/search.cpp b/src/search.cpp
index 866444a8388e29236d50ec4a609a59f11f45df74..5d6babb45f716200c82dd30b2265d9857a0e81b3 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -70,9 +70,9 @@ namespace {
   // Reductions lookup table, initialized at startup
   int Reductions[MAX_MOVES]; // [depth or moveNumber]
 
-  template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
+  Depth reduction(bool i, Depth d, int mn) {
     int r = Reductions[d / ONE_PLY] * Reductions[mn] / 1024;
-    return ((r + 512) / 1024 + (!i && r > 1024) - PvNode) * ONE_PLY;
+    return ((r + 512) / 1024 + (!i && r > 1024)) * ONE_PLY;
   }
 
   constexpr int futility_move_count(bool improving, int depth) {
@@ -964,7 +964,7 @@ moves_loop: // When in check, search starts from here
                   continue;
 
               // Reduced depth of the next LMR search
-              int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
+              int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO);
               lmrDepth /= ONE_PLY;
 
               // Countermoves based pruning (~20 Elo)
@@ -1012,11 +1012,11 @@ moves_loop: // When in check, search starts from here
               || moveCountPruning
               || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha))
       {
-          Depth r = reduction<PvNode>(improving, depth, moveCount);
+          Depth r = reduction(improving, depth, moveCount);
 
           // Decrease reduction if position is or has been on the PV
           if (ttPv)
-              r -= ONE_PLY;
+              r -= 2 * ONE_PLY;
 
           // Decrease reduction if opponent's move count is high (~10 Elo)
           if ((ss-1)->moveCount > 15)