Lazily selects the best move at each step of the search. More...

#include <MovePicker.h>

Public Member Functions
	MovePicker (const Movelist &moves, Move ttMove, const std::array< std::array< Move, 2 >, SearchConstants::MAX_PLY > killers, const std::array< std::array< int, 64 >, 64 > history, const std::array< std::array< int, 64 >, 16 > *captureHist, std::array< Move, MAX_MOVES > &captures, std::array< int, MAX_MOVES > &captureScores, std::array< Move, MAX_MOVES > &quiets, std::array< int, MAX_MOVES > &quietScores, std::array< Move, MAX_MOVES > &badCaptures, int ply, int threadId=0, Move countermove=Move(0))
	Constructs a MovePicker for a specific search node.
Move	nextMove (const Board &board, const Negamax *search, bool inCheck)
	Returns the next best move according to the current phase.
int	scoreMove (const Move &move, const Board &board, const Negamax *search, bool isCapture)
	Scores a move using various heuristics depending on its type.
void	generateAndScoreCaptures (const Board &board, const Negamax *search)
	Generates, scores, and stores all valid capture moves for the current node.
void	generateAndScoreKillers (const Board &board, const Negamax *search)
	Extracts valid killer moves for the current ply and board state.
void	generateAndScoreQuiets (const Board &board, const Negamax *search)
	Generates, scores, and stores all quiet moves for the current node.
template<size_t N>
Move	selectBestMove (std::array< Move, N > &list, std::array< int, N > &scores, int &nextIdx, int count)
	Selects and removes the highest-scoring move from the remaining buffer.

Private Attributes
const Movelist &	allMoves_
	Reference to all legal moves generated for the current node.
std::array< Move, MAX_MOVES > &	captures_
	External buffer for capture moves.
std::array< int, MAX_MOVES > &	captureScores_
	External buffer for capture scores.
int	captureCount_ = 0
	Number of captures populated.
std::array< Move, 2 >	killerMoves_
	Local cache of killer moves for this ply.
int	killerCount_ = 0
	Number of valid killer moves found.
std::array< Move, MAX_MOVES > &	quiets_
	External buffer for quiet moves.
std::array< int, MAX_MOVES > &	quietScores_
	External buffer for quiet scores.
int	quietCount_ = 0
	Number of quiets populated.
Move	ttMove_
	Best move retrieved from the Transposition Table (searched first).
Move	countermove_
	Countermove heuristic response to the opponent's previous move.
const std::array< std::array< Move, 2 >, SearchConstants::MAX_PLY > *	killers_
	Pointer to global killer heuristic table.
const std::array< std::array< int, 64 >, 64 > *	history_
	Pointer to global history heuristic table.
const std::array< std::array< int, 64 >, 16 > *	captureHist_
	Pointer to global capture history table.
int	ply_
	Current distance from root.
int	threadId_
	Thread ID for diversified move ordering in Lazy SMP.
int	nextCapture_ = 0
	Index of the next capture to return.
int	nextKiller_ = 0
	Index of the next killer to return.
int	nextQuiet_ = 0
	Index of the next quiet move to return.
std::array< Move, MAX_MOVES > &	badCaptures_
	External buffer for captures that fail SEE.
int	badCaptureCount_ = 0
	Number of bad captures found.
int	nextBadCapture_ = 0
	Index of the next bad capture to return.
bool	capturesGenerated_ = false
	True if capture moves have been scored and sorted.
bool	killersGenerated_ = false
	True if killer moves have been extracted.
bool	quietsGenerated_ = false
	True if quiet moves have been scored and sorted.
int	nextQueenPromo_ = 0
	Index of the next queen promotion to return.
int	queenPromoCount_ = 0
	Number of queen promotions found.
bool	countermoveReturned_ = false
	True if the countermove has already been returned.
int	phase_ = 0
	Current phase: 0: Promos, 1: TT, 2: Captures, 3: Killers, 4: Countermove, 5: Quiets, 6: Bad Captures.

Static Private Attributes
static constexpr int	MAX_MOVES = 256
	Maximum allowed moves, aligned to power of 2 for safety.

Detailed Description

Lazily selects the best move at each step of the search.

Avoids scoring and sorting all moves upfront, which is crucial for cutoff-heavy nodes. Uses a phased approach: Transposition Table move, Queen Promotions, Good Captures (SEE > 0), Killer Moves, Countermoves, Quiet Moves, and finally Bad Captures (SEE < 0).

Constructor & Destructor Documentation

◆ MovePicker()

MovePicker::MovePicker	(	const Movelist &	moves,
		Move	ttMove,
		const std::array< std::array< Move, 2 >, SearchConstants::MAX_PLY > *	killers,
		const std::array< std::array< int, 64 >, 64 > *	history,
		const std::array< std::array< int, 64 >, 16 > *	captureHist,
		std::array< Move, MAX_MOVES > &	captures,
		std::array< int, MAX_MOVES > &	captureScores,
		std::array< Move, MAX_MOVES > &	quiets,
		std::array< int, MAX_MOVES > &	quietScores,
		std::array< Move, MAX_MOVES > &	badCaptures,
		int	ply,
		int	threadId = 0,
		Move	countermove = Move(0) )

inline

Constructs a MovePicker for a specific search node.

Parameters

moves	Generated legal moves.
ttMove	Best move from TT.
killers	Pointer to killer heuristics.
history	Pointer to history heuristics.
captureHist	Pointer to capture history heuristics.
captures	Pre-allocated buffer for captures.
captureScores	Pre-allocated buffer for capture scores.
quiets	Pre-allocated buffer for quiets.
quietScores	Pre-allocated buffer for quiet scores.
badCaptures	Pre-allocated buffer for bad captures.
ply	Current ply from root.
threadId	Thread ID for diversity.
countermove	Candidate countermove.

Member Function Documentation

◆ generateAndScoreCaptures()

void MovePicker::generateAndScoreCaptures	(	const Board &	board,
		const Negamax *	search )

Generates, scores, and stores all valid capture moves for the current node.

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◆ generateAndScoreKillers()

void MovePicker::generateAndScoreKillers	(	const Board &	board,
		const Negamax *	search )

Extracts valid killer moves for the current ply and board state.

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◆ generateAndScoreQuiets()

void MovePicker::generateAndScoreQuiets	(	const Board &	board,
		const Negamax *	search )

Generates, scores, and stores all quiet moves for the current node.

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◆ nextMove()

Move MovePicker::nextMove	(	const Board &	board,
		const Negamax *	search,
		bool	inCheck )

Returns the next best move according to the current phase.

Lazily processes and sorts moves only when a phase transition occurs.

Parameters

board	The current board state.
search	Pointer to the active Negamax search instance for SEE evaluation.
inCheck	True if the side to move is currently in check.

Returns: The next Move to evaluate, or Move(0) if all moves are exhausted.

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◆ scoreMove()

int MovePicker::scoreMove	(	const Move &	move,
		const Board &	board,
		const Negamax *	search,
		bool	isCapture )

Scores a move using various heuristics depending on its type.

Parameters

move	The move to score.
board	The current board state.
search	Pointer to the Negamax search instance.
isCapture	True if the move is a capture.

Returns: The heuristic score for the move.

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◆ selectBestMove()

template<size_t N>

Move MovePicker::selectBestMove	(	std::array< Move, N > &	list,
		std::array< int, N > &	scores,
		int &	nextIdx,
		int	count )

Selects and removes the highest-scoring move from the remaining buffer.

Template Parameters

N	The size of the buffer.

Parameters

list	The array of moves.
scores	The array of corresponding scores.
nextIdx	The index marking the start of unselected moves.
count	The total number of valid moves in the buffer.

Returns: The best Move.

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Member Data Documentation

◆ allMoves_

const Movelist& MovePicker::allMoves_

private

Reference to all legal moves generated for the current node.

◆ badCaptureCount_

int MovePicker::badCaptureCount_ = 0

private

Number of bad captures found.

◆ badCaptures_

std::array<Move, MAX_MOVES>& MovePicker::badCaptures_

private

External buffer for captures that fail SEE.

◆ captureCount_

int MovePicker::captureCount_ = 0

private

Number of captures populated.

◆ captureHist_

const std::array<std::array<int, 64>, 16>* MovePicker::captureHist_

private

Pointer to global capture history table.

◆ captures_

std::array<Move, MAX_MOVES>& MovePicker::captures_

private

External buffer for capture moves.

◆ captureScores_

std::array<int, MAX_MOVES>& MovePicker::captureScores_

private

External buffer for capture scores.

◆ capturesGenerated_

bool MovePicker::capturesGenerated_ = false

private

True if capture moves have been scored and sorted.

◆ countermove_

Move MovePicker::countermove_

private

Countermove heuristic response to the opponent's previous move.

◆ countermoveReturned_

bool MovePicker::countermoveReturned_ = false

private

True if the countermove has already been returned.

◆ history_

const std::array<std::array<int, 64>, 64>* MovePicker::history_

private

Pointer to global history heuristic table.

◆ killerCount_

int MovePicker::killerCount_ = 0

private

Number of valid killer moves found.

◆ killerMoves_

std::array<Move, 2> MovePicker::killerMoves_

private

Local cache of killer moves for this ply.

◆ killers_

const std::array<std::array<Move, 2>, SearchConstants::MAX_PLY>* MovePicker::killers_

private

Pointer to global killer heuristic table.

◆ killersGenerated_

bool MovePicker::killersGenerated_ = false

private

True if killer moves have been extracted.

◆ MAX_MOVES

int MovePicker::MAX_MOVES = 256

staticconstexprprivate

Maximum allowed moves, aligned to power of 2 for safety.

◆ nextBadCapture_

int MovePicker::nextBadCapture_ = 0

private

Index of the next bad capture to return.

◆ nextCapture_

int MovePicker::nextCapture_ = 0

private

Index of the next capture to return.

◆ nextKiller_

int MovePicker::nextKiller_ = 0

private

Index of the next killer to return.

◆ nextQueenPromo_

int MovePicker::nextQueenPromo_ = 0

private

Index of the next queen promotion to return.

◆ nextQuiet_

int MovePicker::nextQuiet_ = 0

private

Index of the next quiet move to return.

◆ phase_

int MovePicker::phase_ = 0

private

Current phase: 0: Promos, 1: TT, 2: Captures, 3: Killers, 4: Countermove, 5: Quiets, 6: Bad Captures.

◆ ply_

int MovePicker::ply_

private

Current distance from root.

◆ queenPromoCount_

int MovePicker::queenPromoCount_ = 0

private

Number of queen promotions found.

◆ quietCount_

int MovePicker::quietCount_ = 0

private

Number of quiets populated.

◆ quiets_

std::array<Move, MAX_MOVES>& MovePicker::quiets_

private

External buffer for quiet moves.

◆ quietScores_

std::array<int, MAX_MOVES>& MovePicker::quietScores_

private

External buffer for quiet scores.

◆ quietsGenerated_

bool MovePicker::quietsGenerated_ = false

private

True if quiet moves have been scored and sorted.

◆ threadId_

int MovePicker::threadId_

private

Thread ID for diversified move ordering in Lazy SMP.

◆ ttMove_

Move MovePicker::ttMove_

private

Best move retrieved from the Transposition Table (searched first).

The documentation for this class was generated from the following files:

engine/src/search/MovePicker.h
engine/src/search/MovePicker.cpp

Public Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Constructor & Destructor Documentation

◆ MovePicker()

Member Function Documentation

◆ generateAndScoreCaptures()

◆ generateAndScoreKillers()

◆ generateAndScoreQuiets()

◆ nextMove()

◆ scoreMove()

◆ selectBestMove()

Member Data Documentation

◆ allMoves_

◆ badCaptureCount_

◆ badCaptures_

◆ captureCount_

◆ captureHist_

◆ captures_

◆ captureScores_

◆ capturesGenerated_

◆ countermove_

◆ countermoveReturned_

◆ history_

◆ killerCount_

◆ killerMoves_

◆ killers_

◆ killersGenerated_

◆ MAX_MOVES

◆ nextBadCapture_

◆ nextCapture_

◆ nextKiller_

◆ nextQueenPromo_

◆ nextQuiet_

◆ phase_

◆ ply_

◆ queenPromoCount_

◆ quietCount_

◆ quiets_

◆ quietScores_

◆ quietsGenerated_

◆ threadId_

◆ ttMove_