Partial insertion sort

[stockfish] / src / movepick.cpp

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 95e60003f00b6eafc9d5f5592e0cdd22c64bedef..8a4a8b8f75642b7997f4574b6485f8877a54d721 100644 (file)
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -2,7 +2,7 @@
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
-  Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+  Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -34,18 +34,21 @@ namespace {
     QSEARCH_RECAPTURES, QRECAPTURES
   };
 
-  // Our insertion sort, which is guaranteed to be stable, as it should be
-  void insertion_sort(ExtMove* begin, ExtMove* end)
+  // An insertion sort, which sorts moves in descending order up to and including a given limit.
+  // The order of moves smaller than the limit is left unspecified.
+  // To keep the implementation simple, *begin is always included in the list of sorted moves.
+  void partial_insertion_sort(ExtMove* begin, ExtMove* end, Value limit)
   {
-    ExtMove tmp, *p, *q;
-
-    for (p = begin + 1; p < end; ++p)
-    {
-        tmp = *p;
-        for (q = p; q != begin && *(q-1) < tmp; --q)
-            *q = *(q-1);
-        *q = tmp;
-    }
+    for (ExtMove *sortedEnd = begin + 1, *p = begin + 1; p < end; ++p)
+        if (p->value >= limit)
+        {
+            ExtMove tmp = *p, *q;
+            *p = *sortedEnd;
+            for (q = sortedEnd; q != begin && *(q-1) < tmp; --q)
+                *q = *(q-1);
+            *q = tmp;
+            ++sortedEnd;
+        }
   }
 
   // pick_best() finds the best move in the range (begin, end) and moves it to
@@ -111,11 +114,11 @@ MovePicker::MovePicker(const Position& p, Move ttm, Value th)
 
   stage = PROBCUT;
 
-  // In ProbCut we generate captures with SEE higher than the given threshold
+  // In ProbCut we generate captures with SEE higher than or equal to the given threshold
   ttMove =   ttm
           && pos.pseudo_legal(ttm)
           && pos.capture(ttm)
-          && pos.see_ge(ttm, threshold + 1)? ttm : MOVE_NONE;
+          && pos.see_ge(ttm, threshold)? ttm : MOVE_NONE;
 
   stage += (ttMove == MOVE_NONE);
 }
@@ -141,27 +144,24 @@ template<>
 void MovePicker::score<QUIETS>() {
 
   const HistoryStats& history = pos.this_thread()->history;
-  const FromToStats& fromTo = pos.this_thread()->fromTo;
 
-  const CounterMoveStats* cm = (ss-1)->counterMoves;
-  const CounterMoveStats* fm = (ss-2)->counterMoves;
-  const CounterMoveStats* f2 = (ss-4)->counterMoves;
+  const CounterMoveStats& cmh = *(ss-1)->counterMoves;
+  const CounterMoveStats& fmh = *(ss-2)->counterMoves;
+  const CounterMoveStats& fm2 = *(ss-4)->counterMoves;
 
   Color c = pos.side_to_move();
 
   for (auto& m : *this)
-      m.value =      history[pos.moved_piece(m)][to_sq(m)]
-               + (cm ? (*cm)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
-               + (fm ? (*fm)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
-               + (f2 ? (*f2)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
-               + fromTo.get(c, m);
+      m.value =  cmh[pos.moved_piece(m)][to_sq(m)]
+               + fmh[pos.moved_piece(m)][to_sq(m)]
+               + fm2[pos.moved_piece(m)][to_sq(m)]
+               + history.get(c, m);
 }
 
 template<>
 void MovePicker::score<EVASIONS>() {
-  // Try captures ordered by MVV/LVA, then non-captures ordered by history value
+  // Try captures ordered by MVV/LVA, then non-captures ordered by stats heuristics
   const HistoryStats& history = pos.this_thread()->history;
-  const FromToStats& fromTo = pos.this_thread()->fromTo;
   Color c = pos.side_to_move();
 
   for (auto& m : *this)
@@ -169,7 +169,7 @@ void MovePicker::score<EVASIONS>() {
           m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]
                    - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
       else
-          m.value = history[pos.moved_piece(m)][to_sq(m)] + fromTo.get(c, m);
+          m.value = history.get(c, m);
 }
 
 
@@ -178,7 +178,7 @@ void MovePicker::score<EVASIONS>() {
 /// left. It picks the move with the biggest value from a list of generated moves
 /// taking care not to return the ttMove if it has already been searched.
 
-Move MovePicker::next_move() {
+Move MovePicker::next_move(bool skipQuiets) {
 
   Move move;
 
@@ -241,19 +241,17 @@ Move MovePicker::next_move() {
       cur = endBadCaptures;
       endMoves = generate<QUIETS>(pos, cur);
       score<QUIETS>();
-      if (depth < 3 * ONE_PLY)
-      {
-          ExtMove* goodQuiet = std::partition(cur, endMoves, [](const ExtMove& m)
-                                             { return m.value > VALUE_ZERO; });
-          insertion_sort(cur, goodQuiet);
-      } else
-          insertion_sort(cur, endMoves);
+
+      partial_insertion_sort(cur, endMoves,
+                             depth < 3 * ONE_PLY ? VALUE_ZERO : Value(INT_MIN));
       ++stage;
 
   case QUIET:
-      while (cur < endMoves)
+      while (    cur < endMoves
+             && (!skipQuiets || cur->value >= VALUE_ZERO))
       {
           move = *cur++;
+
           if (   move != ttMove
               && move != ss->killers[0]
               && move != ss->killers[1]
@@ -271,8 +269,7 @@ Move MovePicker::next_move() {
   case EVASIONS_INIT:
       cur = moves;
       endMoves = generate<EVASIONS>(pos, cur);
-      if (endMoves - cur - (ttMove != MOVE_NONE) > 1)
-          score<EVASIONS>();
+      score<EVASIONS>();
       ++stage;
 
   case ALL_EVASIONS:
@@ -295,7 +292,7 @@ Move MovePicker::next_move() {
       {
           move = pick_best(cur++, endMoves);
           if (   move != ttMove
-              && pos.see_ge(move, threshold + 1))
+              && pos.see_ge(move, threshold))
               return move;
       }
       break;