History code rewrite (#1122)

Rearrange and rename all history heuristic code. Naming
is now based on chessprogramming.wikispaces.com conventions
and the relations among the various heuristics are now more
clear and consistent.

No functional change.

src/movepick.cpp

@@ -143,11 +143,11 @@ void MovePicker::score<CAPTURES>() {
 template<>
 void MovePicker::score<QUIETS>() {
 
-  const HistoryStats& history = pos.this_thread()->history;
+  const ButterflyHistory& history = pos.this_thread()->history;
 
-  const CounterMoveStats& cmh = *(ss-1)->counterMoves;
+  const PieceToHistory& cmh = *(ss-1)->history;
-  const CounterMoveStats& fmh = *(ss-2)->counterMoves;
+  const PieceToHistory& fmh = *(ss-2)->history;
-  const CounterMoveStats& fm2 = *(ss-4)->counterMoves;
+  const PieceToHistory& fm2 = *(ss-4)->history;
 
   Color c = pos.side_to_move();
 
@@ -155,21 +155,21 @@ void MovePicker::score<QUIETS>() {
       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);
+               + history[c][from_to(m)];
 }
 
 template<>
 void MovePicker::score<EVASIONS>() {
   // Try captures ordered by MVV/LVA, then non-captures ordered by stats heuristics
-  const HistoryStats& history = pos.this_thread()->history;
+  const ButterflyHistory& history = pos.this_thread()->history;
   Color c = pos.side_to_move();
 
   for (auto& m : *this)
       if (pos.capture(m))
           m.value =  PieceValue[MG][pos.piece_on(to_sq(m))]
-                   - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
+                   - Value(type_of(pos.moved_piece(m))) + (1 << 28);
       else
-          m.value = history.get(c, m);
+          m.value = history[c][from_to(m)];
 }
 
 

src/movepick.h

@@ -21,68 +21,70 @@
 #ifndef MOVEPICK_H_INCLUDED
 #define MOVEPICK_H_INCLUDED
 
-#include <cstring>   // For std::memset
+#include <array>
 
 #include "movegen.h"
 #include "position.h"
 #include "types.h"
 
+/// StatBoards is a generic 2-dimensional array used to store various statistics
+template<int Size1, int Size2, typename T = int>
+struct StatBoards : public std::array<std::array<T, Size2>, Size1> {
 
-/// HistoryStats records how often quiet moves have been successful or unsuccessful
+  void fill(const T& v) {
-/// during the current search, and is used for reduction and move ordering decisions.
+    T* p = &(*this)[0][0];
-struct HistoryStats {
+    std::fill(p, p + sizeof(*this) / sizeof(*p), v);
+  }
+};
 
-  static const int Max = 1 << 28;
+/// ButterflyBoards are 2 tables (one for each color) indexed by the move's from
+/// and to squares, see chessprogramming.wikispaces.com/Butterfly+Boards
+typedef StatBoards<COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyBoards;
+
+/// PieceToBoards are addressed by a move's [piece][to] information
+typedef StatBoards<PIECE_NB, SQUARE_NB> PieceToBoards;
+
+/// ButterflyHistory records how often quiet moves have been successful or
+/// unsuccessful during the current search, and is used for reduction and move
+/// ordering decisions. It uses ButterflyBoards as backing store.
+struct ButterflyHistory : public ButterflyBoards {
 
-  int 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, int v) {
 
-    Square from = from_sq(m);
-    Square to = to_sq(m);
-
     const int D = 324;
+    int& entry = (*this)[c][from_to(m)];
 
     assert(abs(v) <= D); // Consistency check for below formula
 
-    table[c][from][to] -= table[c][from][to] * abs(v) / D;
+    entry += v * 32 - entry * abs(v) / D;
-    table[c][from][to] += v * 32;
-  }
 
-private:
+    assert(abs(entry) <= 32 * D);
-  int table[COLOR_NB][SQUARE_NB][SQUARE_NB];
+  }
 };
 
+/// PieceToHistory is like ButterflyHistory, but is based on PieceToBoards
+struct PieceToHistory : public PieceToBoards {
 
-/// 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 update(Piece pc, Square to, Move m) { table[pc][to] = m; }
   void update(Piece pc, Square to, int v) {
 
     const int D = 936;
+    int& entry = (*this)[pc][to];
 
     assert(abs(v) <= D); // Consistency check for below formula
 
-    table[pc][to] -= table[pc][to] * abs(v) / D;
+    entry += v * 32 - entry * abs(v) / D;
-    table[pc][to] += v * 32;
-  }
 
-private:
+    assert(abs(entry) <= 32 * D);
-  T table[PIECE_NB][SQUARE_NB];
+  }
 };
 
-typedef Stats<Move> MoveStats;
+/// CounterMoveStat stores counter moves indexed by [piece][to] of the previous
-typedef Stats<int> CounterMoveStats;
+/// move, see chessprogramming.wikispaces.com/Countermove+Heuristic
-typedef Stats<CounterMoveStats> CounterMoveHistoryStats;
+typedef StatBoards<PIECE_NB, SQUARE_NB, Move> CounterMoveStat;
+
+/// CounterMoveHistoryStat is like CounterMoveStat but instead of a move it
+/// stores a full history (based on PieceTo boards instead of ButterflyBoards).
+typedef StatBoards<PIECE_NB, SQUARE_NB, PieceToHistory> CounterMoveHistoryStat;
 
 
 /// MovePicker class is used to pick one pseudo legal move at a time from the

src/search.cpp

@@ -193,14 +193,15 @@ void Search::clear() {
 
   for (Thread* th : Threads)
   {
-      th->counterMoves.clear();
-      th->history.clear();
-      th->counterMoveHistory.clear();
       th->resetCalls = true;
+      th->counterMoves.fill(MOVE_NONE);
+      th->history.fill(0);
 
-      CounterMoveStats& cm = th->counterMoveHistory[NO_PIECE][0];
+      for (auto& to : th->counterMoveHistory)
-      auto* t = &cm[NO_PIECE][0];
+          for (auto& h : to)
-      std::fill(t, t + sizeof(cm)/sizeof(*t), CounterMovePruneThreshold - 1);
+              h.fill(0);
+
+      th->counterMoveHistory[NO_PIECE][0].fill(CounterMovePruneThreshold - 1);
   }
 
   Threads.main()->previousScore = VALUE_INFINITE;
@@ -334,7 +335,7 @@ void Thread::search() {
 
   std::memset(ss-4, 0, 7 * sizeof(Stack));
   for(int i = 4; i > 0; i--)
-     (ss-i)->counterMoves = &this->counterMoveHistory[NO_PIECE][0]; // Use as sentinel
+     (ss-i)->history = &this->counterMoveHistory[NO_PIECE][0]; // Use as sentinel
 
   bestValue = delta = alpha = -VALUE_INFINITE;
   beta = VALUE_INFINITE;
@@ -558,7 +559,7 @@ namespace {
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
     moveCount = quietCount = ss->moveCount = 0;
-    ss->history = 0;
+    ss->statScore = 0;
     bestValue = -VALUE_INFINITE;
     ss->ply = (ss-1)->ply + 1;
 
@@ -607,7 +608,7 @@ namespace {
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
     ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    ss->counterMoves = &thisThread->counterMoveHistory[NO_PIECE][0];
+    ss->history = &thisThread->counterMoveHistory[NO_PIECE][0];
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
 
@@ -750,7 +751,7 @@ namespace {
         Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
 
         ss->currentMove = MOVE_NULL;
-        ss->counterMoves = &thisThread->counterMoveHistory[NO_PIECE][0];
+        ss->history = &thisThread->counterMoveHistory[NO_PIECE][0];
 
         pos.do_null_move(st);
         Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
@@ -794,7 +795,7 @@ namespace {
             if (pos.legal(move))
             {
                 ss->currentMove = move;
-                ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
+                ss->history = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
 
                 pos.do_move(move, st);
                 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
@@ -818,9 +819,9 @@ namespace {
 
 moves_loop: // When in check search starts from here
 
-    const CounterMoveStats& cmh = *(ss-1)->counterMoves;
+    const PieceToHistory& cmh = *(ss-1)->history;
-    const CounterMoveStats& fmh = *(ss-2)->counterMoves;
+    const PieceToHistory& fmh = *(ss-2)->history;
-    const CounterMoveStats& fm2 = *(ss-4)->counterMoves;
+    const PieceToHistory& fm2 = *(ss-4)->history;
 
     MovePicker mp(pos, ttMove, depth, ss);
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
@@ -956,7 +957,7 @@ moves_loop: // When in check search starts from here
 
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
-      ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
+      ss->history = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
 
       // Step 14. Make the move
       pos.do_move(move, st, givesCheck);
@@ -984,21 +985,21 @@ moves_loop: // When in check search starts from here
                        && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
                   r -= 2 * ONE_PLY;
 
-              ss->history =  cmh[moved_piece][to_sq(move)]
+              ss->statScore =  cmh[moved_piece][to_sq(move)]
-                           + fmh[moved_piece][to_sq(move)]
+                             + fmh[moved_piece][to_sq(move)]
-                           + fm2[moved_piece][to_sq(move)]
+                             + fm2[moved_piece][to_sq(move)]
-                           + thisThread->history.get(~pos.side_to_move(), move)
+                             + thisThread->history[~pos.side_to_move()][from_to(move)]
-                           - 4000; // Correction factor
+                             - 4000; // Correction factor
 
               // Decrease/increase reduction by comparing opponent's stat score
-              if (ss->history > 0 && (ss-1)->history < 0)
+              if (ss->statScore > 0 && (ss-1)->statScore < 0)
                   r -= ONE_PLY;
 
-              else if (ss->history < 0 && (ss-1)->history > 0)
+              else if (ss->statScore < 0 && (ss-1)->statScore > 0)
                   r += ONE_PLY;
 
               // Decrease/increase reduction for moves with a good/bad history
-              r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
+              r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
           }
 
           Depth d = std::max(newDepth - r, ONE_PLY);
@@ -1399,7 +1400,7 @@ moves_loop: // When in check search starts from here
 
     for (int i : {1, 2, 4})
         if (is_ok((ss-i)->currentMove))
-            (ss-i)->counterMoves->update(pc, s, bonus);
+            (ss-i)->history->update(pc, s, bonus);
   }
 
 
@@ -1422,7 +1423,7 @@ moves_loop: // When in check search starts from here
     if (is_ok((ss-1)->currentMove))
     {
         Square prevSq = to_sq((ss-1)->currentMove);
-        thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
+        thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]=move;
     }
 
     // Decrease all the other played quiet moves

src/search.h

@@ -38,13 +38,13 @@ namespace Search {
 
 struct Stack {
   Move* pv;
-  CounterMoveStats* counterMoves;
+  PieceToHistory* history;
   int ply;
   Move currentMove;
   Move excludedMove;
   Move killers[2];
   Value staticEval;
-  int history;
+  int statScore;
   int moveCount;
 };
 

src/thread.h

@@ -68,9 +68,9 @@ public:
   Depth rootDepth;
   Depth completedDepth;
   std::atomic_bool resetCalls;
-  MoveStats counterMoves;
+  CounterMoveStat counterMoves;
-  HistoryStats history;
+  ButterflyHistory history;
-  CounterMoveHistoryStats counterMoveHistory;
+  CounterMoveHistoryStat counterMoveHistory;
 };
 
 

src/types.h

@@ -421,6 +421,10 @@ inline Square to_sq(Move m) {
   return Square(m & 0x3F);
 }
 
+inline int from_to(Move m) {
+ return m & 0xFFF;
+}
+
 inline MoveType type_of(Move m) {
   return MoveType(m & (3 << 14));
 }