Penalty for a quiet ttMove that fails low

VoyagerOne · mcostalba · commit 5254a6040c59 · 2017-01-28T09:32:07.000+01:00
Also the penalty/bonus function is misleading, we
should simply change it to stat_bonus(depth) for
bonus and -stat_bonus(depth+ ONE_PLY) for extra
penalty.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 11656 W: 2183 L: 2008 D: 7465

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 11152 W: 1531 L: 1377 D: 8244

Bench: 6101931
diff --git a/src/search.cpp b/src/search.cpp
@@ -75,6 +75,12 @@ namespace {
     return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
   }
 
+  // History and stats update bonus, based on depth
+  Value stat_bonus(Depth depth) {
+    int d = depth / ONE_PLY ;
+    return Value(d * d + 2 * d - 2);
+  }
+
   // Skill structure is used to implement strength limit
   struct Skill {
     Skill(int l) : level(l) {}
@@ -155,9 +161,6 @@ namespace {
 
   const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
 
-  Value bonus(Depth depth)   { int d = depth / ONE_PLY ; return  Value(d * d + 2 * d - 2); }
-  Value penalty(Depth depth) { int d = depth / ONE_PLY ; return -Value(d * d + 4 * d + 1); }
-
   EasyMoveManager EasyMove;
   Value DrawValue[COLOR_NB];
 
@@ -642,14 +645,24 @@ namespace {
                             : (tte->bound() & BOUND_UPPER)))
     {
         // If ttMove is quiet, update move sorting heuristics on TT hit
-        if (ttValue >= beta && ttMove)
+        if (ttMove)
         {
-            if (!pos.capture_or_promotion(ttMove))
-                update_stats(pos, ss, ttMove, nullptr, 0, bonus(depth));
+            if (ttValue >= beta)
+            {
+                if (!pos.capture_or_promotion(ttMove))
+                    update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
 
-            // Extra penalty for a quiet TT move in previous ply when it gets refuted
-            if ((ss-1)->moveCount == 1 && !pos.captured_piece())
-                update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, penalty(depth));
+                // Extra penalty for a quiet TT move in previous ply when it gets refuted
+                if ((ss-1)->moveCount == 1 && !pos.captured_piece())
+                    update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+            }
+            // Penalty for a quiet ttMove that fails low
+            else if (ttValue < alpha && !pos.capture_or_promotion(ttMove))
+            {
+                Value penalty = -stat_bonus(depth + ONE_PLY);
+                thisThread->history.update(pos.side_to_move(), ttMove, penalty);
+                update_cm_stats(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
+            }
         }
         return ttValue;
     }
@@ -988,7 +1001,7 @@ namespace {
                            + (fmh  ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
                            + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
                            + thisThread->history.get(~pos.side_to_move(), move)
-                           - 8000; // Correction factor
+                           - 4000; // Correction factor
 
               // Decrease/increase reduction by comparing opponent's stat score
               if (ss->history > VALUE_ZERO && (ss-1)->history < VALUE_ZERO)
@@ -1120,17 +1133,17 @@ namespace {
 
         // Quiet best move: update move sorting heuristics
         if (!pos.capture_or_promotion(bestMove))
-            update_stats(pos, ss, bestMove, quietsSearched, quietCount, bonus(depth));
+            update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
 
         // Extra penalty for a quiet TT move in previous ply when it gets refuted
         if ((ss-1)->moveCount == 1 && !pos.captured_piece())
-            update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, penalty(depth));
+            update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
     }
     // Bonus for prior countermove that caused the fail low
     else if (    depth >= 3 * ONE_PLY
              && !pos.captured_piece()
              && is_ok((ss-1)->currentMove))
-        update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, bonus(depth));
+        update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
 
     tte->save(posKey, value_to_tt(bestValue, ss->ply),
               bestValue >= beta ? BOUND_LOWER :
