+
+// 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.
+ constexpr double as[] = {0.38036525, -2.82015070, 23.17882135, 307.36768407};
+ constexpr double bs[] = {-2.29434733, 13.27689788, -14.26828904, 63.45318330};
+
+ // Enforce that NormalizeToPawnValue corresponds to a 50% win rate at ply 64
+ static_assert(UCI::NormalizeToPawnValue == int(as[0] + as[1] + as[2] + as[3]));
+
+ 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(v), -4000.0, 4000.0);
+
+ // Return the win rate in per mille units, rounded to the nearest integer
+ return int(0.5 + 1000 / (1 + std::exp((a - x) / b)));
+}
+
+} // namespace
+
+
+// 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;
+ std::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(std::cin, cmd)) // Wait for an input or an end-of-file (EOF) indication
+ cmd = "quit";
+
+ std::istringstream is(cmd);
+
+ token.clear(); // Avoid a stale if getline() returns nothing or a blank line
+ is >> std::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 >> std::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
+}
+
+
+// Turns a Value to an integer centipawn number,
+// without treatment of mate and similar special scores.
+int UCI::to_cp(Value v) { return 100 * v / UCI::NormalizeToPawnValue; }
+
+// 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'.
+std::string UCI::value(Value v) {
+
+ assert(-VALUE_INFINITE < v && v < VALUE_INFINITE);
+
+ std::stringstream ss;
+
+ if (std::abs(v) < VALUE_TB_WIN_IN_MAX_PLY)
+ ss << "cp " << UCI::to_cp(v);
+ else if (std::abs(v) <= VALUE_TB)
+ {
+ const int ply = VALUE_TB - std::abs(v); // recompute ss->ply
+ ss << "cp " << (v > 0 ? 20000 - ply : -20000 + ply);
+ }
+ else
+ ss << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
+
+ return ss.str();
+}
+
+
+// Reports the win-draw-loss (WDL) statistics given an evaluation
+// and a game ply based on the data gathered for fishtest LTC games.
+std::string UCI::wdl(Value v, int ply) {
+
+ std::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();
+}
+
+
+// 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))};
+}
+
+
+// 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'.
+std::string UCI::move(Move m, bool chess960) {
+
+ if (m == MOVE_NONE)
+ return "(none)";
+
+ if (m == MOVE_NULL)
+ return "0000";
+
+ Square from = from_sq(m);
+ Square to = to_sq(m);
+
+ if (type_of(m) == CASTLING && !chess960)
+ to = make_square(to > from ? FILE_G : FILE_C, rank_of(from));
+
+ std::string move = UCI::square(from) + UCI::square(to);
+
+ if (type_of(m) == PROMOTION)
+ move += " pnbrqk"[promotion_type(m)];
+
+ return 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, std::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