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Rewrite Position::from_fen()

Browse source 
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>
This commit is contained in:
Marco Costalba 2010-07-23 10:38:19 +02:00
parent 098ac5e44e
commit 839088205e
4 changed files with 146 additions and 112 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
src/benchmark.cpp
View file

@ -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",
"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"
};

2
src/material.cpp
View file

@ -404,7 +404,7 @@ Key EndgameFunctions::buildKey(const string& keyCode) {
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();
}

253
src/position.cpp
View file

@ -26,6 +26,7 @@
#include <cstring>
#include <fstream>
#include <iostream>
#include <sstream>
#include "bitcount.h"
#include "mersenne.h"
@ -38,6 +39,8 @@
#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) {
/*
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 };
clear();
// Board
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
file += (fen[i] - '1' + 1);
file += token - '1' + 1;
continue;
}
else if (fen[i] == '/')
else if (token == '/')
{
file = FILE_A;
rank--;
continue;
}
size_t idx = pieceLetters.find(fen[i]);
idx = pieceLetters.find(token);
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++;
}
// 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;
if (!set_castling_rights(token))
goto incorrect_fen;
}
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++;
}
// 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);
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;
@ -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);
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;
std::cout << std::endl;
cout << endl;
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--)
{
std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
cout << "+---+---+---+---+---+---+---+---+" << endl;
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 ? '=' : ' ');
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;
}
@ -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 (Square sq = SQ_A1; sq <= SQ_H8; sq++)
castleRightsMask[sq] = ALL_CASTLES;
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;
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;

1
src/position.h
View file

@ -294,6 +294,7 @@ private:
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);