Refine SEE threshold for capture pruning.

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index afc4a671251b03c196d1d07a565561158f9524df..f0783363e79766fc682dabbf42fc4d0d0cda9469 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -31,8 +31,8 @@
 #include "movepick.h"
 #include "position.h"
 #include "search.h"
-#include "timeman.h"
 #include "thread.h"
+#include "timeman.h"
 #include "tt.h"
 #include "uci.h"
 #include "syzygy/tbprobe.h"
@@ -63,16 +63,25 @@ namespace {
   enum NodeType { NonPV, PV };
 
   // Sizes and phases of the skip-blocks, used for distributing search depths across the threads
-  const int SkipSize[]  = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
-  const int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
+  constexpr int SkipSize[]  = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
+  constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
 
   // Razor and futility margins
-  const int RazorMargin1 = 590;
-  const int RazorMargin2 = 604;
+  constexpr int RazorMargin[] = {0, 590, 604};
   Value futility_margin(Depth d, bool improving) {
     return Value((175 - 50 * improving) * d / ONE_PLY);
   }
 
+  // Margin for pruning capturing moves: almost linear in depth
+  constexpr int CapturePruneMargin[] = { 0,
+                                         1 * PawnValueEg * 1055 / 1000,
+                                         2 * PawnValueEg * 1042 / 1000,
+                                         3 * PawnValueEg * 963  / 1000,
+                                         4 * PawnValueEg * 1038 / 1000,
+                                         5 * PawnValueEg * 950  / 1000,
+                                         6 * PawnValueEg * 930  / 1000
+                                       };
+
   // Futility and reductions lookup tables, initialized at startup
   int FutilityMoveCounts[2][16]; // [improving][depth]
   int Reductions[2][2][64][64];  // [pv][improving][depth][moveNumber]
@@ -161,7 +170,7 @@ void Search::init() {
               Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
 
               // Increase reduction for non-PV nodes when eval is not improving
-              if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
+              if (!imp && r > 1.0)
                 Reductions[NonPV][imp][d][mc]++;
           }
 
@@ -310,8 +319,8 @@ void Thread::search() {
   multiPV = std::min(multiPV, rootMoves.size());
 
   int ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns
-  Eval::Contempt = (us == WHITE ?  make_score(ct, ct / 2)
-                                : -make_score(ct, ct / 2));
+  contempt = (us == WHITE ?  make_score(ct, ct / 2)
+                          : -make_score(ct, ct / 2));
 
   // Iterative deepening loop until requested to stop or the target depth is reached
   while (   (rootDepth += ONE_PLY) < DEPTH_MAX
@@ -344,17 +353,18 @@ void Thread::search() {
           // Reset aspiration window starting size
           if (rootDepth >= 5 * ONE_PLY)
           {
+              Value previousScore = rootMoves[PVIdx].previousScore;
               delta = Value(18);
-              alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
-              beta  = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
+              alpha = std::max(previousScore - delta,-VALUE_INFINITE);
+              beta  = std::min(previousScore + delta, VALUE_INFINITE);
 
               ct =  Options["Contempt"] * PawnValueEg / 100; // From centipawns
 
-              // Adjust contempt based on current bestValue (dynamic contempt)
-              ct += int(std::round(48 * atan(float(bestValue) / 128)));
+              // Adjust contempt based on root move's previousScore (dynamic contempt)
+              ct += int(std::round(48 * atan(float(previousScore) / 128)));
 
-              Eval::Contempt = (us == WHITE ?  make_score(ct, ct / 2)
-                                            : -make_score(ct, ct / 2));
+              contempt = (us == WHITE ?  make_score(ct, ct / 2)
+                                      : -make_score(ct, ct / 2));
           }
 
           // Start with a small aspiration window and, in the case of a fail
@@ -690,21 +700,13 @@ namespace {
 
     // Step 7. Razoring (skipped when in check)
     if (  !PvNode
-        && depth <= 2 * ONE_PLY)
+        && depth < 3 * ONE_PLY
+        && eval <= alpha - RazorMargin[depth / ONE_PLY])
     {
-        if (   depth == ONE_PLY
-            && eval + RazorMargin1 <= alpha)
-            return qsearch<NonPV>(pos, ss, alpha, alpha+1);
-
-        else if (eval + RazorMargin2 <= alpha)
-        {
-            Value ralpha = alpha - RazorMargin2;
-
-            Value v = qsearch<NonPV>(pos, ss, ralpha, ralpha+1);
-
-            if (v <= ralpha)
-                return v;
-        }
+        Value ralpha = alpha - (depth >= 2 * ONE_PLY) * RazorMargin[depth / ONE_PLY];
+        Value v = qsearch<NonPV>(pos, ss, ralpha, ralpha+1);
+        if (depth < 2 * ONE_PLY || v <= ralpha)
+            return v;
     }
 
     // Step 8. Futility pruning: child node (skipped when in check)
@@ -800,7 +802,7 @@ namespace {
     // Step 11. Internal iterative deepening (skipped when in check)
     if (    depth >= 6 * ONE_PLY
         && !ttMove
-        && (PvNode || ss->staticEval + 256 >= beta))
+        && (PvNode || ss->staticEval + 128 >= beta))
     {
         Depth d = 3 * depth / 4 - 2 * ONE_PLY;
         search<NT>(pos, ss, alpha, beta, d, cutNode, true);
@@ -927,7 +929,7 @@ moves_loop: // When in check, search starts from here
           }
           else if (    depth < 7 * ONE_PLY
                    && !extension
-                   && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
+                   && !pos.see_ge(move, -Value(CapturePruneMargin[depth / ONE_PLY])))
                   continue;
       }
 
@@ -1157,7 +1159,6 @@ moves_loop: // When in check, search starts from here
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
 
     constexpr bool PvNode = NT == PV;
-    const bool inCheck = bool(pos.checkers());
 
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
@@ -1171,7 +1172,7 @@ moves_loop: // When in check, search starts from here
     Move ttMove, move, bestMove;
     Depth ttDepth;
     Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
-    bool ttHit, givesCheck, evasionPrunable;
+    bool ttHit, inCheck, givesCheck, evasionPrunable;
     int moveCount;
 
     if (PvNode)
@@ -1183,6 +1184,7 @@ moves_loop: // When in check, search starts from here
 
     (ss+1)->ply = ss->ply + 1;
     ss->currentMove = bestMove = MOVE_NONE;
+    inCheck = pos.checkers();
     moveCount = 0;
 
     // Check for an immediate draw or maximum ply reached
@@ -1504,7 +1506,7 @@ void MainThread::check_time() {
 
   static TimePoint lastInfoTime = now();
 
-  int elapsed = Time.elapsed();
+  TimePoint elapsed = Time.elapsed();
   TimePoint tick = Limits.startTime + elapsed;
 
   if (tick - lastInfoTime >= 1000)
@@ -1530,7 +1532,7 @@ void MainThread::check_time() {
 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
 
   std::stringstream ss;
-  int elapsed = Time.elapsed() + 1;
+  TimePoint elapsed = Time.elapsed() + 1;
   const RootMoves& rootMoves = pos.this_thread()->rootMoves;
   size_t PVIdx = pos.this_thread()->PVIdx;
   size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());