scid::core::move_predicates Namespace Reference

Stateless helpers used by Position move validation. More...

Functions
bool	valid_king (squareT sqFrom, squareT sqTo)
	Returns true when the two squares are a king move apart.
bool	valid_knight (squareT sqFrom, squareT sqTo)
	Returns true when the two squares form a knight move.
int	valid_slider (squareT sqFrom, squareT sqTo, pieceT pieceType)
	Returns the slider step from sqFrom to sqTo.
bool	attack_pawn (squareT sqFrom, squareT sqTo, colorT pieceCol)
	Returns true when a pawn of pieceCol attacks sqTo from sqFrom.
template<typename TFunc >
bool	attack_slider (squareT sqFrom, squareT sqTo, pieceT pieceType, TFunc isOccupied)
	Returns true when a slider attacks along an unobstructed ray.
template<typename TFunc >
bool	attack (squareT sqFrom, squareT sqTo, pieceT pieceCol, pieceT pieceType, TFunc isOccupied)
	Validates an attack move.
template<typename TFunc >
bool	pseudo_advance_pawn (squareT sqFrom, squareT sqTo, colorT pieceCol, TFunc isOccupied)
	Validates a non-capturing pawn advance.
template<typename TFunc >
bool	pseudo (squareT sqFrom, squareT sqTo, colorT pieceCol, pieceT pieceType, TFunc isOccupied)
	Validates pseudo-legal movement using piece geometry and occupancy.
template<typename TFunc >
std::pair< pieceT, squareT >	opens_ray (squareT sqFrom, squareT sqTo, squareT sqRay, TFunc isOccupied)
	Finds a possible discovered pin caused by moving from a ray.
bool	blocks_ray (squareT sqFrom, squareT sqTo, squareT sqBlock)
	Tests whether sqBlock lies between two ray-aligned squares.

Variables
constexpr int	NSQUARES = 8
constexpr int	kWPHomeRank = 1
constexpr int	kBPHomeRank = NSQUARES - 2

Detailed Description

Stateless helpers used by Position move validation.

These helpers separate chess movement into four levels:

• A valid move follows piece geometry alone, such as a bishop moving diagonally. Validity does not require a position.
• An attack move is valid capture geometry plus blocker checks for sliders and pawn capture direction. It needs only an occupancy predicate.
• A pseudo-legal move is an attack move, a non-capture pawn advance, or a castle candidate.
• A legal move is pseudo-legal, does not land on a friendly piece, and does not leave the mover's king in check. Legal move validation belongs to Position because it needs full board state.

Function Documentation

attack()

template<typename TFunc >

bool scid::core::move_predicates::attack	(	squareT	sqFrom,
		squareT	sqTo,
		pieceT	pieceCol,
		pieceT	pieceType,
		TFunc	isOccupied
	)

Validates an attack move.

Parameters

sqFrom	square of the attacking piece.
sqTo	square being attacked.
pieceCol	colour of the attacking piece.
pieceType	type of the attacking piece.
isOccupied	callable returning true when an intermediate square is occupied. It is not called for sqFrom or sqTo, so it can describe either the pre-move or post-move occupancy of those endpoint squares.

Returns

true when the piece attacks sqTo from sqFrom.

attack_slider()

template<typename TFunc >

bool scid::core::move_predicates::attack_slider	(	squareT	sqFrom,
		squareT	sqTo,
		pieceT	pieceType,
		TFunc	isOccupied
	)

Returns true when a slider attacks along an unobstructed ray.

isOccupied is called only for squares strictly between sqFrom and sqTo.

blocks_ray()

bool scid::core::move_predicates::blocks_ray ( squareT  sqFrom, squareT  sqTo, squareT  sqBlock  )

inline

Tests whether sqBlock lies between two ray-aligned squares.

Returns

true when a piece on sqBlock would block a queen ray from sqFrom to sqTo.

opens_ray()

template<typename TFunc >

std::pair< pieceT, squareT > scid::core::move_predicates::opens_ray ( squareT  sqFrom, squareT  sqTo, squareT  sqRay, TFunc  isOccupied  )

inline

Finds a possible discovered pin caused by moving from a ray.

Given a pseudo-legal move, this returns the kind and square of the first piece that may pin the mover to sqRay, usually the mover's king square.

Parameters

sqFrom	origin square of the pseudo-legal move.
sqTo	destination square of the pseudo-legal move.
sqRay	square through which the projected ray passes.
isOccupied	callable returning true when a square is occupied.

Returns

a pair of candidate attacker type and square. INVALID_PIECE means no ray was opened. Otherwise, the caller must inspect the returned square: an enemy queen or an enemy piece matching the returned type makes the move illegal.

pseudo()

template<typename TFunc >

bool scid::core::move_predicates::pseudo	(	squareT	sqFrom,
		squareT	sqTo,
		colorT	pieceCol,
		pieceT	pieceType,
		TFunc	isOccupied
	)

Validates pseudo-legal movement using piece geometry and occupancy.

This covers attacks and non-capturing pawn advances. Castling is handled by Position because castling rights, rook identity, and attacked transit squares require full position state.

pseudo_advance_pawn()

template<typename TFunc >

bool scid::core::move_predicates::pseudo_advance_pawn ( squareT  sqFrom, squareT  sqTo, colorT  pieceCol, TFunc  isOccupied  )

inline

Validates a non-capturing pawn advance.

Single and home-rank double advances are accepted when every traversed square is empty according to isOccupied.

valid_slider()

int scid::core::move_predicates::valid_slider ( squareT  sqFrom, squareT  sqTo, pieceT  pieceType  )

inline

Returns the slider step from sqFrom to sqTo.

Returns

the signed-independent board step for a queen, rook, or bishop ray, or 0 when pieceType cannot move along that ray.