Retire history[]

Use key saved in state instead.

No functional change (in real games) and no speed regression.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/position.cpp

@@ -99,7 +99,6 @@ CheckInfo::CheckInfo(const Position& pos) {
 Position::Position(const Position& pos, int th) {
 
   memcpy(this, &pos, sizeof(Position));
-  detach(); // Always detach() in copy c'tor to avoid surprises
   threadID = th;
   nodes = 0;
 
@@ -113,18 +112,6 @@ Position::Position(const string& fen, bool isChess960, int th) {
 }
 
 
-/// Position::detach() copies the content of the current state and castling
-/// masks inside the position itself. This is needed when the st pointee could
-/// become stale, as example because the caller is about to going out of scope.
-
-void Position::detach() {
-
-  startState = *st;
-  st = &startState;
-  st->previous = NULL; // As a safe guard
-}
-
-
 /// Position::from_fen() initializes the position object with the given FEN
 /// string. This function is not very robust - make sure that input FENs are
 /// correct (this is assumed to be the responsibility of the GUI).
@@ -775,27 +762,16 @@ bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
 /// Position::do_setup_move() makes a permanent move on the board. It should
 /// be used when setting up a position on board. You can't undo the move.
 
-void Position::do_setup_move(Move m) {
+void Position::do_setup_move(Move m, StateInfo& newSt) {
 
   assert(move_is_ok(m));
 
-  StateInfo newSt;
-
   // Update the number of full moves after black's move
   if (sideToMove == BLACK)
       fullMoves++;
 
   do_move(m, newSt);
 
-  // Reset "game ply" in case we made a non-reversible move.
-  // "game ply" is used for repetition detection.
-  if (st->rule50 == 0)
-      st->gamePly = 0;
-
-  // Our StateInfo newSt is about going out of scope so copy
-  // its content before it disappears.
-  detach();
-
   assert(is_ok());
 }
 
@@ -834,16 +810,13 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   newSt.previous = st;
   st = &newSt;
 
-  // Save the current key to the history[] array, in order to be able to
-  // detect repetition draws.
-  history[st->gamePly++] = key;
-
   // Update side to move
   key ^= zobSideToMove;
 
   // Increment the 50 moves rule draw counter. Resetting it to zero in the
   // case of non-reversible moves is taken care of later.
   st->rule50++;
+  st->gamePly++;
   st->pliesFromNull++;
 
   if (move_is_castle(m))
@@ -1369,10 +1342,6 @@ void Position::do_null_move(StateInfo& backupSt) {
   backupSt.pliesFromNull = st->pliesFromNull;
   st->previous = &backupSt;
 
-  // Save the current key to the history[] array, in order to be able to
-  // detect repetition draws.
-  history[st->gamePly++] = st->key;
-
   // Update the necessary information
   if (st->epSquare != SQ_NONE)
       st->key ^= zobEp[st->epSquare];
@@ -1383,6 +1352,7 @@ void Position::do_null_move(StateInfo& backupSt) {
   sideToMove = opposite_color(sideToMove);
   st->epSquare = SQ_NONE;
   st->rule50++;
+  st->gamePly++;
   st->pliesFromNull = 0;
   st->value += (sideToMove == WHITE) ?  TempoValue : -TempoValue;
 
@@ -1699,9 +1669,24 @@ bool Position::is_draw() const {
 
   // Draw by repetition?
   if (!SkipRepetition)
-      for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
-          if (history[st->gamePly - i] == st->key)
-              return true;
+  {
+      int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull);
+
+      if (i <= e)
+      {
+          StateInfo* stp = st->previous->previous;
+
+          do {
+              stp = stp->previous->previous;
+
+              if (stp->key == st->key)
+                  return true;
+
+              i +=2;
+
+          } while (i <= e);
+      }
+  }
 
   return false;
 }

src/position.h

@@ -26,11 +26,6 @@
 #include "move.h"
 #include "types.h"
 
-/// Maximum number of plies per game (220 should be enough, because the
-/// maximum search depth is 100, and during position setup we reset the
-/// move counter for every non-reversible move).
-const int MaxGameLength = 220;
-
 
 /// The checkInfo struct is initialized at c'tor time and keeps info used
 /// to detect if a move gives check.
@@ -168,7 +163,7 @@ public:
   bool pawn_is_passed(Color c, Square s) const;
 
   // Doing and undoing moves
-  void do_setup_move(Move m);
+  void do_setup_move(Move m, StateInfo& st);
   void do_move(Move m, StateInfo& st);
   void do_move(Move m, StateInfo& st, const CheckInfo& ci, bool moveIsCheck);
   void undo_move(Move m);
@@ -219,7 +214,6 @@ private:
 
   // Initialization helper functions (used while setting up a position)
   void clear();
-  void detach();
   void put_piece(Piece p, Square s);
   void set_castle(int f, Square ksq, Square rsq);
   void set_castling_rights(char token);
@@ -258,7 +252,6 @@ private:
   int index[64];               // [square]
 
   // Other info
-  Key history[MaxGameLength];
   int castleRightsMask[64];    // [square]
   Square castleRookSquare[16]; // [castleRight]
   StateInfo startState;

src/uci.cpp

@@ -21,6 +21,7 @@
 #include <iostream>
 #include <sstream>
 #include <string>
+#include <vector>
 
 #include "evaluate.h"
 #include "misc.h"
@@ -36,6 +37,10 @@ namespace {
   // FEN string for the initial position
   const string StartPositionFEN = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
 
+  // Keep track of position keys along the setup moves (from start position to the
+  // position just before to start searching). This is needed by draw detection.
+  std::vector<StateInfo> SetupState;
+
   // UCIParser is a class for parsing UCI input. The class
   // is actually a string stream built on a given input string.
   typedef istringstream UCIParser;
@@ -140,8 +145,13 @@ namespace {
     else return;
 
     // Parse move list (if any)
+    SetupState.clear();
+
     while (up >> token && (m = move_from_uci(pos, token)) != MOVE_NONE)
-        pos.do_setup_move(m);
+    {
+        SetupState.push_back(StateInfo());
+        pos.do_setup_move(m, SetupState.back());
+    }
   }