simplify logic for history based pruning

[stockfish] / src / movepick.h

diff --git a/src/movepick.h b/src/movepick.h
index 9482a89c491f7fa792771e88e52a9a5c3a0a3879..ef3be6c240f8d553b42c68756e48fa512b5bdf3d 100644 (file)
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -2,6 +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) 2015-2017 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
@@ -25,51 +26,65 @@
 
 #include "movegen.h"
 #include "position.h"
-#include "search.h"
 #include "types.h"
 
 
-/// The Stats struct stores moves statistics. According to the template parameter
-/// the class can store History, Gains and Countermoves. History records how often
-/// different moves have been successful or unsuccessful during the current search
-/// and is used for reduction and move ordering decisions. Gains records the move's
-/// best evaluation gain from one ply to the next and is used for pruning decisions.
-/// Countermoves store the move that refute a previous one. Entries are stored
-/// using only the moving piece and destination square, hence two moves with
-/// different origin but same destination and piece will be considered identical.
-template<bool Gain, typename T>
-struct Stats {
+/// HistoryStats records how often quiet moves have been successful or unsuccessful
+/// during the current search, and is used for reduction and move ordering decisions.
+struct HistoryStats {
 
-  static const Value Max = Value(250);
+  static const Value Max = Value(1 << 28);
 
-  const T* operator[](Piece pc) const { return table[pc]; }
+  Value get(Color c, Move m) const { return table[c][from_sq(m)][to_sq(m)]; }
   void clear() { std::memset(table, 0, sizeof(table)); }
+  void update(Color c, Move m, Value v) {
+
+    Square from = from_sq(m);
+    Square to = to_sq(m);
 
-  void update(Piece pc, Square to, Move m) {
+    const int denom = 324;
 
-    if (m == table[pc][to].first)
-        return;
+    assert(abs(int(v)) <= denom); // Needed for stability.
 
-    table[pc][to].second = table[pc][to].first;
-    table[pc][to].first = m;
+    table[c][from][to] -= table[c][from][to] * abs(int(v)) / denom;
+    table[c][from][to] += int(v) * 32;
   }
 
+private:
+  Value table[COLOR_NB][SQUARE_NB][SQUARE_NB];
+};
+
+
+/// A template struct, used to generate MoveStats and CounterMoveHistoryStats:
+/// MoveStats store the move that refute a previous one.
+/// CounterMoveHistoryStats is like HistoryStats, but with two consecutive moves.
+/// Entries are stored using only the moving piece and destination square, hence
+/// two moves with different origin but same destination and piece will be
+/// considered identical.
+template<typename T>
+struct Stats {
+  const T* operator[](Piece pc) const { return table[pc]; }
+  T* operator[](Piece pc) { return table[pc]; }
+  void clear() { std::memset(table, 0, sizeof(table)); }
+  void fill(const Value& v) { std::fill(&table[0][0], &table[PIECE_NB-1][SQUARE_NB-1]+1, v); };
+  void update(Piece pc, Square to, Move m) { table[pc][to] = m; }
   void update(Piece pc, Square to, Value v) {
 
-    if (Gain)
-        table[pc][to] = std::max(v, table[pc][to] - 1);
+    const int denom = 936;
+
+    assert(abs(int(v)) <= denom); // Needed for stability.
 
-    else if (abs(table[pc][to] + v) < Max)
-        table[pc][to] +=  v;
+    table[pc][to] -= table[pc][to] * abs(int(v)) / denom;
+    table[pc][to] += int(v) * 32;
   }
 
 private:
   T table[PIECE_NB][SQUARE_NB];
 };
 
-typedef Stats< true, Value> GainsStats;
-typedef Stats<false, Value> HistoryStats;
-typedef Stats<false, std::pair<Move, Move> > MovesStats;
+typedef Stats<Move> MoveStats;
+typedef Stats<Value> CounterMoveStats;
+typedef Stats<CounterMoveStats> CounterMoveHistoryStats;
 
 
 /// MovePicker class is used to pick one pseudo legal move at a time from the
@@ -78,34 +93,33 @@ typedef Stats<false, std::pair<Move, Move> > MovesStats;
 /// when MOVE_NONE is returned. In order to improve the efficiency of the alpha
 /// beta algorithm, MovePicker attempts to return the moves which are most likely
 /// to get a cut-off first.
+namespace Search { struct Stack; }
 
 class MovePicker {
 public:
   MovePicker(const MovePicker&) = delete;
   MovePicker& operator=(const MovePicker&) = delete;
 
-  MovePicker(const Position&, Move, Depth, const HistoryStats&, Square);
-  MovePicker(const Position&, Move, const HistoryStats&, PieceType);
-  MovePicker(const Position&, Move, Depth, const HistoryStats&, Move*, Move*, Search::Stack*);
+  MovePicker(const Position&, Move, Value);
+  MovePicker(const Position&, Move, Depth, Square);
+  MovePicker(const Position&, Move, Depth, Search::Stack*);
 
-  template<bool SpNode> Move next_move();
+  Move next_move(bool skipQuiets = false);
 
 private:
   template<GenType> void score();
-  void generate_next_stage();
+  ExtMove* begin() { return cur; }
+  ExtMove* end() { return endMoves; }
 
   const Position& pos;
-  const HistoryStats& history;
-  Search::Stack* ss;
-  Move* countermoves;
-  Move* followupmoves;
+  const Search::Stack* ss;
+  Move countermove;
   Depth depth;
   Move ttMove;
-  ExtMove killers[6];
   Square recaptureSquare;
-  Value captureThreshold;
+  Value threshold;
   int stage;
-  ExtMove *cur, *end, *endQuiets, *endBadCaptures;
+  ExtMove *cur, *endMoves, *endBadCaptures;
   ExtMove moves[MAX_MOVES];
 };