Rewrite Position::from_fen()

Complete rewrite the function and extend compatibility
also to X-FEN notation for Chess960.

We are now able to read standard FEN, Shredder-FEN and X-FEN.

No functional change.

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

diff --git a/src/benchmark.cpp b/src/benchmark.cpp
index e23afb1422cd2709427f0d69f3e9c050bc7ec776..c554008b857f3b46d50fc66ab501a8c8c85ab82d 100644 (file)
--- a/src/benchmark.cpp
+++ b/src/benchmark.cpp
@@ -51,7 +51,7 @@ const string BenchmarkPositions[] = {
   "r1bq1r1k/b1p1npp1/p2p3p/1p6/3PP3/1B2NN2/PP3PPP/R2Q1RK1 w - - 1 16",
   "3r1rk1/p5pp/bpp1pp2/8/q1PP1P2/b3P3/P2NQRPP/1R2B1K1 b - - 6 22",
   "r1q2rk1/2p1bppp/2Pp4/p6b/Q1PNp3/4B3/PP1R1PPP/2K4R w - - 2 18",
   "r1bq1r1k/b1p1npp1/p2p3p/1p6/3PP3/1B2NN2/PP3PPP/R2Q1RK1 w - - 1 16",
   "3r1rk1/p5pp/bpp1pp2/8/q1PP1P2/b3P3/P2NQRPP/1R2B1K1 b - - 6 22",
   "r1q2rk1/2p1bppp/2Pp4/p6b/Q1PNp3/4B3/PP1R1PPP/2K4R w - - 2 18",

-  "4k2r/1pb2ppp/1p2p3/1R1p4/3P4/2r1PN2/P4PPP/1R4K1 b  - 3 22",
+  "4k2r/1pb2ppp/1p2p3/1R1p4/3P4/2r1PN2/P4PPP/1R4K1 b - - 3 22",

   "3q2k1/pb3p1p/4pbp1/2r5/PpN2N2/1P2P2P/5PP1/Q2R2K1 b - - 4 26"
 };
 
   "3q2k1/pb3p1p/4pbp1/2r5/PpN2N2/1P2P2P/5PP1/Q2R2K1 b - - 4 26"
 };
 

diff --git a/src/material.cpp b/src/material.cpp
index 973d3684715fcabc8ba91cb66334f44a63039423..03db87c876c66b7c2e981f19eb29633a528616ad 100644 (file)
--- a/src/material.cpp
+++ b/src/material.cpp
@@ -404,7 +404,7 @@ Key EndgameFunctions::buildKey(const string& keyCode) {
 
         s << char(upcase ? toupper(keyCode[i]) : tolower(keyCode[i]));
     }
 
         s << char(upcase ? toupper(keyCode[i]) : tolower(keyCode[i]));
     }

-    s << 8 - keyCode.length() << "/8/8/8/8/8/8/8 w -";
+    s << 8 - keyCode.length() << "/8/8/8/8/8/8/8 w - -";

     return Position(s.str(), 0).get_material_key();
 }
 
     return Position(s.str(), 0).get_material_key();
 }
 

diff --git a/src/position.cpp b/src/position.cpp
index 537e574f51e4bc723cd85a3a50545de216f88b22..1942abb0823c4add37a29bc8764319f4e4ec5578 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -26,6 +26,7 @@
 #include <cstring>
 #include <fstream>
 #include <iostream>
 #include <cstring>
 #include <fstream>
 #include <iostream>

+#include <sstream>

 
 #include "bitcount.h"
 #include "mersenne.h"
 
 #include "bitcount.h"
 #include "mersenne.h"


@@ -38,6 +39,8 @@
 #include "ucioption.h"
 
 using std::string;
 #include "ucioption.h"
 
 using std::string;

+using std::cout;
+using std::endl;

 
 
 ////
 
 
 ////


@@ -111,135 +114,104 @@ void Position::detach() {
 /// correct (this is assumed to be the responsibility of the GUI).
 
 void Position::from_fen(const string& fen) {
 /// correct (this is assumed to be the responsibility of the GUI).
 
 void Position::from_fen(const string& fen) {

+/*
+   A FEN string defines a particular position using only the ASCII character set.
+
+   A FEN string contains six fields. The separator between fields is a space. The fields are:
+
+   1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
+      with rank 1; within each rank, the contents of each square are described from file a through file h.
+      Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
+      from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
+      while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
+      of blank squares), and "/" separate ranks.
+
+   2) Active color. "w" means white moves next, "b" means black.
+
+   3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
+      letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
+      kingside), and/or "q" (Black can castle queenside).
+
+   4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
+      If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
+      regardless of whether there is a pawn in position to make an en passant capture.
+
+   5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
+      to determine if a draw can be claimed under the fifty-move rule.
+
+   6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
+*/

 
   static const string pieceLetters = "KQRBNPkqrbnp";
   static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
 
 
   static const string pieceLetters = "KQRBNPkqrbnp";
   static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
 

-  clear();
-
-  // Board

   Rank rank = RANK_8;
   File file = FILE_A;
   Rank rank = RANK_8;
   File file = FILE_A;

-  size_t i = 0;
-  for ( ; fen[i] != ' '; i++)
+  size_t idx;
+
+  std::istringstream ss(fen);
+  char token;
+
+  clear();
+
+  // 1. Piece placement field
+  while (ss.get(token) && token != ' ')

   {
   {

-      if (isdigit(fen[i]))
+      if (isdigit(token))

       {
           // Skip the given number of files
       {
           // Skip the given number of files

-          file += (fen[i] - '1' + 1);
+          file += token - '1' + 1;

           continue;
       }
           continue;
       }

-      else if (fen[i] == '/')
+      else if (token == '/')

       {
           file = FILE_A;
           rank--;
           continue;
       }
       {
           file = FILE_A;
           rank--;
           continue;
       }

-      size_t idx = pieceLetters.find(fen[i]);
+
+      idx = pieceLetters.find(token);

       if (idx == string::npos)
       if (idx == string::npos)

-      {
-           std::cout << "Error in FEN at character " << i << std::endl;
-           return;
-      }
-      Square square = make_square(file, rank);
-      put_piece(pieces[idx], square);
+          goto incorrect_fen;
+
+      put_piece(pieces[idx], make_square(file, rank));

       file++;
   }
 
       file++;
   }
 

-  // Side to move
-  i++;
-  if (fen[i] != 'w' && fen[i] != 'b')
-  {
-      std::cout << "Error in FEN at character " << i << std::endl;
-      return;
-  }
-  sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
+  // 2. Active color
+  if (!ss.get(token) || (token != 'w' && token != 'b'))
+      goto incorrect_fen;

 
 

-  // Castling rights
-  i++;
-  if (fen[i] != ' ')
+  sideToMove = (token == 'w' ? WHITE : BLACK);
+
+  if (!ss.get(token) || token != ' ')
+      goto incorrect_fen;
+
+  // 3. Castling availability
+  while (ss.get(token) && token != ' ')

   {
   {

-      std::cout << "Error in FEN at character " << i << std::endl;
-      return;
-  }
+      if (token == '-')
+          continue;

 
 

-  i++;
-  while (strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
-      if (fen[i] == '-')
-      {
-          i++;
-          break;
-      }
-      else if (fen[i] == 'K') allow_oo(WHITE);
-      else if (fen[i] == 'Q') allow_ooo(WHITE);
-      else if (fen[i] == 'k') allow_oo(BLACK);
-      else if (fen[i] == 'q') allow_ooo(BLACK);
-      else if (fen[i] >= 'A' && fen[i] <= 'H') {
-          File rookFile, kingFile = FILE_NONE;
-          for (Square square = SQ_B1; square <= SQ_G1; square++)
-              if (piece_on(square) == WK)
-                  kingFile = square_file(square);
-          if (kingFile == FILE_NONE) {
-              std::cout << "Error in FEN at character " << i << std::endl;
-              return;
-          }
-          initialKFile = kingFile;
-          rookFile = File(fen[i] - 'A') + FILE_A;
-          if (rookFile < initialKFile) {
-              allow_ooo(WHITE);
-              initialQRFile = rookFile;
-          }
-          else {
-              allow_oo(WHITE);
-              initialKRFile = rookFile;
-          }
-      }
-      else if (fen[i] >= 'a' && fen[i] <= 'h') {
-          File rookFile, kingFile = FILE_NONE;
-          for (Square square = SQ_B8; square <= SQ_G8; square++)
-              if (piece_on(square) == BK)
-                  kingFile = square_file(square);
-          if (kingFile == FILE_NONE) {
-              std::cout << "Error in FEN at character " << i << std::endl;
-              return;
-          }
-          initialKFile = kingFile;
-          rookFile = File(fen[i] - 'a') + FILE_A;
-          if (rookFile < initialKFile) {
-              allow_ooo(BLACK);
-              initialQRFile = rookFile;
-          }
-          else {
-              allow_oo(BLACK);
-              initialKRFile = rookFile;
-          }
-      }
-      else {
-          std::cout << "Error in FEN at character " << i << std::endl;
-          return;
-      }
-      i++;
+      if (!set_castling_rights(token))
+          goto incorrect_fen;

   }
 
   }
 

-  // Skip blanks
-  while (fen[i] == ' ')
-      i++;
-
-  // En passant square -- ignore if no capture is possible
-  if (    i <= fen.length() - 2
-      && (fen[i] >= 'a' && fen[i] <= 'h')
-      && (fen[i+1] == '3' || fen[i+1] == '6'))
+  // 4. En passant square -- ignore if no capture is possible
+  char col, row;
+  if (   (ss.get(col) && (col >= 'a' && col <= 'h'))
+      && (ss.get(row) && (row == '3' || row == '6')))

   {
   {

-      Square fenEpSquare = square_from_string(fen.substr(i, 2));
+      Square fenEpSquare = make_square(file_from_char(col), rank_from_char(row));

       Color them = opposite_color(sideToMove);
       Color them = opposite_color(sideToMove);

+

       if (attacks_from<PAWN>(fenEpSquare, them) & this->pieces(PAWN, sideToMove))
       if (attacks_from<PAWN>(fenEpSquare, them) & this->pieces(PAWN, sideToMove))

-          st->epSquare = square_from_string(fen.substr(i, 2));
+          st->epSquare = fenEpSquare;

   }
 
   }
 

-  // Various initialisation
-  for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
-      castleRightsMask[sq] = ALL_CASTLES;
+  // 5-6. Halfmove clock and fullmove number are not parsed

 
 

+  // Various initialisations

   castleRightsMask[make_square(initialKFile,  RANK_1)] ^= (WHITE_OO|WHITE_OOO);
   castleRightsMask[make_square(initialKFile,  RANK_8)] ^= (BLACK_OO|BLACK_OOO);
   castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
   castleRightsMask[make_square(initialKFile,  RANK_1)] ^= (WHITE_OO|WHITE_OOO);
   castleRightsMask[make_square(initialKFile,  RANK_8)] ^= (BLACK_OO|BLACK_OOO);
   castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;


@@ -255,6 +227,67 @@ void Position::from_fen(const string& fen) {
   st->value = compute_value();
   st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
   st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
   st->value = compute_value();
   st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
   st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);

+  return;
+
+incorrect_fen:
+  cout << "Error in FEN string: " << fen << endl;
+}
+
+
+/// Position::set_castling_rights() sets castling parameters castling avaiability.
+/// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
+/// that uses the letters of the columns on which the rooks began the game instead
+/// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
+/// associated with the castling right, the traditional castling tag will be replaced
+/// by the file letter of the involved rook as for the Shredder-FEN.
+
+bool Position::set_castling_rights(char token) {
+
+    Color c = token >= 'a' ? BLACK : WHITE;
+    Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
+    Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
+    Piece rook = (c == WHITE ? WR : BR);
+
+    initialKFile = square_file(king_square(c));
+    token = char(toupper(token));
+
+    if (token == 'K')
+    {
+        for (Square sq = sqH; sq >= sqA; sq--)
+            if (piece_on(sq) == rook)
+            {
+                allow_oo(c);
+                initialKRFile = square_file(sq);
+                break;
+            }
+    }
+    else if (token == 'Q')
+    {
+        for (Square sq = sqA; sq <= sqH; sq++)
+            if (piece_on(sq) == rook)
+            {
+                allow_ooo(c);
+                initialQRFile = square_file(sq);
+                break;
+            }
+    }
+    else if (token >= 'A' && token <= 'H')
+    {
+        File rookFile = File(token - 'A') + FILE_A;
+        if (rookFile < initialKFile)
+        {
+            allow_ooo(c);
+            initialQRFile = rookFile;
+        }
+        else
+        {
+            allow_oo(c);
+            initialKRFile = rookFile;
+        }
+    }
+    else return false;
+
+  return true;

 }
 
 
 }
 
 


@@ -337,16 +370,16 @@ void Position::print(Move m) const {
 
   RequestPending = true;
 
 
   RequestPending = true;
 

-  std::cout << std::endl;
+  cout << endl;

   if (m != MOVE_NONE)
   {
       Position p(*this, thread());
       string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
   if (m != MOVE_NONE)
   {
       Position p(*this, thread());
       string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");

-      std::cout << "Move is: " << col << move_to_san(p, m) << std::endl;
+      cout << "Move is: " << col << move_to_san(p, m) << endl;

   }
   for (Rank rank = RANK_8; rank >= RANK_1; rank--)
   {
   }
   for (Rank rank = RANK_8; rank >= RANK_1; rank--)
   {

-      std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
+      cout << "+---+---+---+---+---+---+---+---+" << endl;

       for (File file = FILE_A; file <= FILE_H; file++)
       {
           Square sq = make_square(file, rank);
       for (File file = FILE_A; file <= FILE_H; file++)
       {
           Square sq = make_square(file, rank);


@@ -355,13 +388,13 @@ void Position::print(Move m) const {
               piece = NO_PIECE;
 
           char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
               piece = NO_PIECE;
 
           char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');

-          std::cout << '|' << col << pieceLetters[piece] << col;
+          cout << '|' << col << pieceLetters[piece] << col;

       }
       }

-      std::cout << '|' << std::endl;
+      cout << '|' << endl;

   }
   }

-  std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
-            << "Fen is: " << to_fen() << std::endl
-            << "Key is: " << st->key << std::endl;
+  cout << "+---+---+---+---+---+---+---+---+" << endl
+            << "Fen is: " << to_fen() << endl
+            << "Key is: " << st->key << endl;

 
   RequestPending = false;
 }
 
   RequestPending = false;
 }


@@ -1474,6 +1507,9 @@ void Position::clear() {
       for (int j = 0; j < 16; j++)
           pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
 
       for (int j = 0; j < 16; j++)
           pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
 

+  for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
+      castleRightsMask[sq] = ALL_CASTLES;
+

   sideToMove = WHITE;
   initialKFile = FILE_E;
   initialKRFile = FILE_H;
   sideToMove = WHITE;
   initialKFile = FILE_E;
   initialKRFile = FILE_H;


@@ -1799,9 +1835,6 @@ void Position::flipped_copy(const Position& pos) {
   initialKRFile = pos.initialKRFile;
   initialQRFile = pos.initialQRFile;
 
   initialKRFile = pos.initialKRFile;
   initialQRFile = pos.initialQRFile;
 

-  for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
-      castleRightsMask[sq] = ALL_CASTLES;
-

   castleRightsMask[make_square(initialKFile,  RANK_1)] ^= (WHITE_OO | WHITE_OOO);
   castleRightsMask[make_square(initialKFile,  RANK_8)] ^= (BLACK_OO | BLACK_OOO);
   castleRightsMask[make_square(initialKRFile, RANK_1)] ^=  WHITE_OO;
   castleRightsMask[make_square(initialKFile,  RANK_1)] ^= (WHITE_OO | WHITE_OOO);
   castleRightsMask[make_square(initialKFile,  RANK_8)] ^= (BLACK_OO | BLACK_OOO);
   castleRightsMask[make_square(initialKRFile, RANK_1)] ^=  WHITE_OO;

diff --git a/src/position.h b/src/position.h
index 826fa13bfa85233cfe7931e4606e237ffa6bede8..4854b29dcf876dcf64d98c08ff1e8cc69784c85d 100644 (file)
--- a/src/position.h
+++ b/src/position.h
@@ -294,6 +294,7 @@ private:
   void put_piece(Piece p, Square s);
   void allow_oo(Color c);
   void allow_ooo(Color c);
   void put_piece(Piece p, Square s);
   void allow_oo(Color c);
   void allow_ooo(Color c);

+  bool set_castling_rights(char token);

 
   // Helper functions for doing and undoing moves
   void do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep);
 
   // Helper functions for doing and undoing moves
   void do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep);