/*

Stockfish, a UCI chess playing engine derived from Glaurung 2.1

Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file)

Stockfish is free software: you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation, either version 3 of the License, or

(at your option) any later version.

Stockfish is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program. If not, see <http://www.gnu.org/licenses/>.

*/

#include <cassert>

#include <cmath>

#include <iostream>

#include <sstream>

#include <string>

#include "evaluate.h"

#include "movegen.h"

#include "position.h"

#include "search.h"

#include "thread.h"

#include "timeman.h"

#include "tt.h"

#include "uci.h"

#include "syzygy/tbprobe.h"

using namespace std;

namespace Stockfish {

extern vector<string> setup_bench(const Position&, istream&);

namespace {

// FEN string for the initial position in standard chess

const char* StartFEN = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";

// position() is called when the engine receives the "position" UCI command.

// It sets up the position that is described in the given FEN string ("fen") or

// the initial position ("startpos") and then makes the moves given in the following

// move list ("moves").

void position(Position& pos, istringstream& is, StateListPtr& states) {

Move m;

string token, fen;

is >> token;

if (token == "startpos")

{

fen = StartFEN;

is >> token; // Consume the "moves" token, if any

}

else if (token == "fen")

while (is >> token && token != "moves")

fen += token + " ";

else

return;

states = StateListPtr(new std::deque<StateInfo>(1)); // Drop the old state and create a new one

pos.set(fen, Options["UCI_Chess960"], &states->back(), Threads.main());

// Parse the move list, if any

while (is >> token && (m = UCI::to_move(pos, token)) != MOVE_NONE)

{

states->emplace_back();

pos.do_move(m, states->back());

}

}

// trace_eval() prints the evaluation of the current position, consistent with

// the UCI options set so far.

void trace_eval(Position& pos) {

StateListPtr states(new std::deque<StateInfo>(1));

Position p;

p.set(pos.fen(), Options["UCI_Chess960"], &states->back(), Threads.main());

Eval::NNUE::verify();

sync_cout << "\n" << Eval::trace(p) << sync_endl;

}

// setoption() is called when the engine receives the "setoption" UCI command.

// The function updates the UCI option ("name") to the given value ("value").

void setoption(istringstream& is) {

string token, name, value;

is >> token; // Consume the "name" token

// Read the option name (can contain spaces)

while (is >> token && token != "value")

name += (name.empty() ? "" : " ") + token;

// Read the option value (can contain spaces)

while (is >> token)

value += (value.empty() ? "" : " ") + token;

if (Options.count(name))

Options[name] = value;

else

sync_cout << "No such option: " << name << sync_endl;

}

// go() is called when the engine receives the "go" UCI command. The function

// sets the thinking time and other parameters from the input string, then starts

// with a search.

void go(Position& pos, istringstream& is, StateListPtr& states) {

Search::LimitsType limits;

string token;

bool ponderMode = false;

limits.startTime = now(); // The search starts as early as possible

while (is >> token)

if (token == "searchmoves") // Needs to be the last command on the line

while (is >> token)

limits.searchmoves.push_back(UCI::to_move(pos, token));

else if (token == "wtime") is >> limits.time[WHITE];

else if (token == "btime") is >> limits.time[BLACK];

else if (token == "winc") is >> limits.inc[WHITE];

else if (token == "binc") is >> limits.inc[BLACK];

else if (token == "movestogo") is >> limits.movestogo;

else if (token == "depth") is >> limits.depth;

else if (token == "nodes") is >> limits.nodes;

else if (token == "movetime") is >> limits.movetime;

else if (token == "mate") is >> limits.mate;

else if (token == "perft") is >> limits.perft;

else if (token == "infinite") limits.infinite = 1;

else if (token == "ponder") ponderMode = true;

Threads.start_thinking(pos, states, limits, ponderMode);

}

// bench() is called when the engine receives the "bench" command.

// Firstly, a list of UCI commands is set up according to the bench

// parameters, then it is run one by one, printing a summary at the end.

void bench(Position& pos, istream& args, StateListPtr& states) {

string token;

uint64_t num, nodes = 0, cnt = 1;

vector<string> list = setup_bench(pos, args);

num = count_if(list.begin(), list.end(), [](string s) { return s.find("go ") == 0 || s.find("eval") == 0; });

TimePoint elapsed = now();

for (const auto& cmd : list)

{

istringstream is(cmd);

is >> skipws >> token;

if (token == "go" || token == "eval")

{

cerr << "\nPosition: " << cnt++ << '/' << num << " (" << pos.fen() << ")" << endl;

if (token == "go")

{

go(pos, is, states);

Threads.main()->wait_for_search_finished();

nodes += Threads.nodes_searched();

}

else

trace_eval(pos);

}

else if (token == "setoption") setoption(is);

else if (token == "position") position(pos, is, states);

else if (token == "ucinewgame") { Search::clear(); elapsed = now(); } // Search::clear() may take a while

}

elapsed = now() - elapsed + 1; // Ensure positivity to avoid a 'divide by zero'

dbg_print();

cerr << "\n==========================="

<< "\nTotal time (ms) : " << elapsed

<< "\nNodes searched : " << nodes

<< "\nNodes/second : " << 1000 * nodes / elapsed << endl;

}

// The win rate model returns the probability of winning (in per mille units) given an

// eval and a game ply. It fits the LTC fishtest statistics rather accurately.

int win_rate_model(Value v, int ply) {

// The model only captures up to 240 plies, so limit the input and then rescale

double m = std::min(240, ply) / 64.0;

// The coefficients of a third-order polynomial fit is based on the fishtest data

// for two parameters that need to transform eval to the argument of a logistic

// function.

double as[] = {-1.17202460e-01, 5.94729104e-01, 1.12065546e+01, 1.22606222e+02};

double bs[] = {-1.79066759, 11.30759193, -17.43677612, 36.47147479};

double a = (((as[0] * m + as[1]) * m + as[2]) * m) + as[3];

double b = (((bs[0] * m + bs[1]) * m + bs[2]) * m) + bs[3];

// Transform the eval to centipawns with limited range

double x = std::clamp(double(100 * v) / PawnValueEg, -2000.0, 2000.0);

// Return the win rate in per mille units rounded to the nearest value

return int(0.5 + 1000 / (1 + std::exp((a - x) / b)));

}

} // namespace

void UCI::set_position(Position& pos, const string& strpos) {

static StateListPtr states;

states = StateListPtr(new std::deque<StateInfo>(1)); // Drop old and create a new one

pos.set(strpos, Options["UCI_Chess960"], &states->back(), Threads.main());

}

/// UCI::loop() waits for a command from the stdin, parses it and then calls the appropriate

/// function. It also intercepts an end-of-file (EOF) indication from the stdin to ensure a

/// graceful exit if the GUI dies unexpectedly. When called with some command-line arguments,

/// like running 'bench', the function returns immediately after the command is executed.

/// In addition to the UCI ones, some additional debug commands are also supported.

void UCI::loop(int argc, char* argv[]) {

Position pos;

string token, cmd;

StateListPtr states(new std::deque<StateInfo>(1));

pos.set(StartFEN, false, &states->back(), Threads.main());

for (int i = 1; i < argc; ++i)

cmd += std::string(argv[i]) + " ";

do {

if (argc == 1 && !getline(cin, cmd)) // Wait for an input or an end-of-file (EOF) indication

cmd = "quit";

istringstream is(cmd);

token.clear(); // Avoid a stale if getline() returns nothing or a blank line

is >> skipws >> token;

if ( token == "quit"

|| token == "stop")

Threads.stop = true;

// The GUI sends 'ponderhit' to tell that the user has played the expected move.

// So, 'ponderhit' is sent if pondering was done on the same move that the user

// has played. The search should continue, but should also switch from pondering

// to the normal search.

else if (token == "ponderhit")

Threads.main()->ponder = false; // Switch to the normal search

else if (token == "uci")

sync_cout << "id name " << engine_info(true)

<< "\n" << Options

<< "\nuciok" << sync_endl;

else if (token == "setoption") setoption(is);

else if (token == "go") go(pos, is, states);

else if (token == "position") position(pos, is, states);

else if (token == "ucinewgame") Search::clear();

else if (token == "isready") sync_cout << "readyok" << sync_endl;

// Add custom non-UCI commands, mainly for debugging purposes.

// These commands must not be used during a search!

else if (token == "flip") pos.flip();

else if (token == "bench") bench(pos, is, states);

else if (token == "d") sync_cout << pos << sync_endl;

else if (token == "eval") trace_eval(pos);

else if (token == "compiler") sync_cout << compiler_info() << sync_endl;

else if (token == "export_net")

{

std::optional<std::string> filename;

std::string f;

if (is >> skipws >> f)

filename = f;

Eval::NNUE::save_eval(filename);

}

else if (token == "--help" || token == "help" || token == "--license" || token == "license")

sync_cout << "\nStockfish is a powerful chess engine for playing and analyzing."

"\nIt is released as free software licensed under the GNU GPLv3 License."

"\nStockfish is normally used with a graphical user interface (GUI) and implements"

"\nthe Universal Chess Interface (UCI) protocol to communicate with a GUI, an API, etc."

"\nFor any further information, visit https://github.com/official-stockfish/Stockfish#readme"

"\nor read the corresponding README.md and Copying.txt files distributed along with this program.\n" << sync_endl;

else if (!token.empty() && token[0] != '#')

sync_cout << "Unknown command: '" << cmd << "'. Type help for more information." << sync_endl;

} while (token != "quit" && argc == 1); // The command-line arguments are one-shot

}

/// UCI::value() converts a Value to a string by adhering to the UCI protocol specification:

///

/// cp <x> The score from the engine's point of view in centipawns.

/// mate <y> Mate in 'y' moves (not plies). If the engine is getting mated,

/// uses negative values for 'y'.

string UCI::value(Value v) {

assert(-VALUE_INFINITE < v && v < VALUE_INFINITE);

stringstream ss;

if (abs(v) < VALUE_MATE_IN_MAX_PLY)

ss << "cp " << v * 100 / PawnValueEg;

else

ss << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;

return ss.str();

}

/// UCI::wdl() reports the win-draw-loss (WDL) statistics given an evaluation

/// and a game ply based on the data gathered for fishtest LTC games.

string UCI::wdl(Value v, int ply) {

stringstream ss;

int wdl_w = win_rate_model( v, ply);

int wdl_l = win_rate_model(-v, ply);

int wdl_d = 1000 - wdl_w - wdl_l;

ss << " wdl " << wdl_w << " " << wdl_d << " " << wdl_l;

return ss.str();

}

/// UCI::square() converts a Square to a string in algebraic notation (g1, a7, etc.)

std::string UCI::square(Square s) {

return std::string{ char('a' + file_of(s)), char('1' + rank_of(s)) };

}

/// UCI::move() converts a Move to a string in coordinate notation (g1f3, a7a8q).

/// The only special case is castling where the e1g1 notation is printed in

/// standard chess mode and in e1h1 notation it is printed in Chess960 mode.

/// Internally, all castling moves are always encoded as 'king captures rook'.

string UCI::move(Move m, bool chess960) {

Square from = from_sq(m);

Square to = to_sq(m);

if (m == MOVE_NONE)

return "(none)";

if (m == MOVE_NULL)

return "0000";

if (type_of(m) == CASTLING && !chess960)

to = make_square(to > from ? FILE_G : FILE_C, rank_of(from));

string move = UCI::square(from) + UCI::square(to);

if (type_of(m) == PROMOTION)

move += " pnbrqk"[promotion_type(m)];

return move;

}

/// UCI::to_move() converts a string representing a move in coordinate notation

/// (g1f3, a7a8q) to the corresponding legal Move, if any.

Move UCI::to_move(const Position& pos, string& str) {

if (str.length() == 5)

str[4] = char(tolower(str[4])); // The promotion piece character must be lowercased

for (const auto& m : MoveList<LEGAL>(pos))

if (str == UCI::move(m, pos.is_chess960()))

return m;

return MOVE_NONE;

}

} // namespace Stockfish