/*

Stockfish, a UCI chess playing engine derived from Glaurung 2.1

Copyright (C) 2004-2008 Tord Romstad (Glaurung author)

Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad

Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad

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 <algorithm>

#include <cfloat>

#include <cmath>

#include "search.h"

#include "timeman.h"

#include "uci.h"

TimeManagement Time; // Our global time management object

namespace {

enum TimeType { OptimumTime, MaxTime };

constexpr int MoveHorizon = 50; // Plan time management at most this many moves ahead

constexpr double MaxRatio = 7.3; // When in trouble, we can step over reserved time with this ratio

constexpr double StealRatio = 0.34; // However we must not steal time from remaining moves over this ratio

// move_importance() is a skew-logistic function based on naive statistical

// analysis of "how many games are still undecided after n half-moves". Game

// is considered "undecided" as long as neither side has >275cp advantage.

// Data was extracted from the CCRL game database with some simple filtering criteria.

double move_importance(int ply) {

constexpr double XScale = 6.85;

constexpr double XShift = 64.5;

constexpr double Skew = 0.171;

return pow((1 + exp((ply - XShift) / XScale)), -Skew) + DBL_MIN; // Ensure non-zero

}

template<TimeType T>

TimePoint remaining(TimePoint myTime, int movesToGo, int ply, TimePoint slowMover) {

constexpr double TMaxRatio = (T == OptimumTime ? 1.0 : MaxRatio);

constexpr double TStealRatio = (T == OptimumTime ? 0.0 : StealRatio);

double moveImportance = (move_importance(ply) * slowMover) / 100.0;

double otherMovesImportance = 0.0;

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

otherMovesImportance += move_importance(ply + 2 * i);

double ratio1 = (TMaxRatio * moveImportance) / (TMaxRatio * moveImportance + otherMovesImportance);

double ratio2 = (moveImportance + TStealRatio * otherMovesImportance) / (moveImportance + otherMovesImportance);

return TimePoint(myTime * std::min(ratio1, ratio2)); // Intel C++ asks for an explicit cast

}

} // namespace

/// init() is called at the beginning of the search and calculates the allowed

/// thinking time out of the time control and current game ply. We support four

/// different kinds of time controls, passed in 'limits':

///

/// inc == 0 && movestogo == 0 means: x basetime [sudden death!]

/// inc == 0 && movestogo != 0 means: x moves in y minutes

/// inc > 0 && movestogo == 0 means: x basetime + z increment

/// inc > 0 && movestogo != 0 means: x moves in y minutes + z increment

void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {

TimePoint minThinkingTime = Options["Minimum Thinking Time"];

TimePoint moveOverhead = Options["Move Overhead"];

TimePoint slowMover = Options["Slow Mover"];

TimePoint npmsec = Options["nodestime"];

TimePoint hypMyTime;

// If we have to play in 'nodes as time' mode, then convert from time

// to nodes, and use resulting values in time management formulas.

// WARNING: to avoid time losses, the given npmsec (nodes per millisecond)

// must be much lower than the real engine speed.

if (npmsec)

{

if (!availableNodes) // Only once at game start

availableNodes = npmsec * limits.time[us]; // Time is in msec

// Convert from milliseconds to nodes

limits.time[us] = TimePoint(availableNodes);

limits.inc[us] *= npmsec;

limits.npmsec = npmsec;

}

startTime = limits.startTime;

optimumTime = maximumTime = std::max(limits.time[us], minThinkingTime);

const int maxMTG = limits.movestogo ? std::min(limits.movestogo, MoveHorizon) : MoveHorizon;

// We calculate optimum time usage for different hypothetical "moves to go" values

// and choose the minimum of calculated search time values. Usually the greatest

// hypMTG gives the minimum values.

for (int hypMTG = 1; hypMTG <= maxMTG; ++hypMTG)

{

// Calculate thinking time for hypothetical "moves to go"-value

hypMyTime = limits.time[us]

+ limits.inc[us] * (hypMTG - 1)

- moveOverhead * (2 + std::min(hypMTG, 40));

hypMyTime = std::max(hypMyTime, TimePoint(0));

TimePoint t1 = minThinkingTime + remaining<OptimumTime>(hypMyTime, hypMTG, ply, slowMover);

TimePoint t2 = minThinkingTime + remaining<MaxTime >(hypMyTime, hypMTG, ply, slowMover);

optimumTime = std::min(t1, optimumTime);

maximumTime = std::min(t2, maximumTime);

}

if (Options["Ponder"])

optimumTime += optimumTime / 4;

}