Documentation
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Overview ¶
Package movegen contains functionality to create moves on a chess position. It implements several variants like generate pseudo legal moves, legal moves or on demand generation of pseudo legal moves.
Index ¶
- type GenMode
- type Movegen
- func (mg *Movegen) GenerateLegalMoves(position *position.Position, mode GenMode) *moveslice.MoveSlice
- func (mg *Movegen) GeneratePseudoLegalMoves(p *position.Position, mode GenMode, evasion bool) *moveslice.MoveSlice
- func (mg *Movegen) GetMoveFromSan(posPtr *position.Position, sanMove string) Move
- func (mg *Movegen) GetMoveFromUci(posPtr *position.Position, uciMove string) Move
- func (mg *Movegen) GetNextMove(p *position.Position, mode GenMode, evasion bool) Move
- func (mg *Movegen) HasLegalMove(position *position.Position) bool
- func (mg *Movegen) KillerMoves() *[2]Move
- func (mg *Movegen) PvMove() Move
- func (mg *Movegen) ResetOnDemand()
- func (mg *Movegen) SetHistoryData(historyData *history.History)
- func (mg *Movegen) SetPvMove(move Move)
- func (mg *Movegen) StoreKiller(move Move)
- func (mg *Movegen) String() string
- func (mg *Movegen) ValidateMove(p *position.Position, move Move) bool
- type Perft
Constants ¶
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Variables ¶
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Functions ¶
This section is empty.
Types ¶
type Movegen ¶
type Movegen struct {
// contains filtered or unexported fields
}
Movegen data structure. Create new move generator via
movegen.NewMoveGen()
Creating this directly will not work.
func NewMoveGen ¶
func NewMoveGen() *Movegen
NewMoveGen creates a new instance of a move generator This is the only time when we allocate new memory. The instance will not create any move lists during normal move generation as it will reuse pre-created internal lists which will be returned via pointer to a caller. OBS: Be careful when trying to store the list of generated moves as the underlying list will be changed when move gen is called again. A deep copy is necessary if you need a copy of the move list. For a deep copy use:
moveslice.MoveSlice.Clone()
func (*Movegen) GenerateLegalMoves ¶
func (mg *Movegen) GenerateLegalMoves(position *position.Position, mode GenMode) *moveslice.MoveSlice
GenerateLegalMoves generates legal moves for the next player. Uses GeneratePseudoLegalMoves and filters out illegal moves. Usually only used for root moves generation as this is expensive. During the AlphaBeta search we will only use pseudo legal move generation.
func (*Movegen) GeneratePseudoLegalMoves ¶
func (mg *Movegen) GeneratePseudoLegalMoves(p *position.Position, mode GenMode, evasion bool) *moveslice.MoveSlice
GeneratePseudoLegalMoves generates pseudo moves for the next player. Does not check if king is left in check or if it passes an attacked square when castling or has been in check before castling.
If a PV move is set with setPV(Move pv) this move will be returned first and will not be returned at its normal place.
Killer moves will be played as soon as possible after non quiet moves. As Killer moves are stored for the whole ply a Killer move might not be valid for the current position. Therefore we need to wait until they are generated. Killer moves will then be pushed to the top of the the quiet moves.
Evasion is a parameter given when the position is in check and only evasion moves should be generated. For testing purposes this is a parameter but obviously we could determine checks very quickly internally in this function. The idea of evasion is to avoid generating moves which are obviously not getting the king out of check. This may reduce the total number of generated moves but there might still be a few non legal moves. This is the case if considering and calculating all possible scenarios is more expensive than to just generate the move and dismiss is later. Because of beta cuts off we quite often will never have to check the full legality of these moves anyway.
func (*Movegen) GetMoveFromSan ¶
GetMoveFromSan Generates all legal moves and matches the given SAN move string against them. If there is a match the actual move is returned. Otherwise MoveNone is returned.
As this uses string creation and comparison this is not very efficient. Use only when performance is not critical.
func (*Movegen) GetMoveFromUci ¶
GetMoveFromUci Generates all legal moves and matches the given UCI move string against them. If there is a match the actual move is returned. Otherwise MoveNone is returned.
As this uses string creation and comparison this is not very efficient. Use only when performance is not critical.
func (*Movegen) GetNextMove ¶
GetNextMove is the main function for phased generation of pseudo legal moves. It returns the next move for the given position and will usually be called in a loop during search. As we hope for an early beta cut this will save time as not all moves will have been generated.
To reuse this on the same position a call to ResetOnDemand() is necessary. This is not necessary when a different position is called as this func will reset it self in this case.
If a PV move is set with setPV(Move pv) this will be returned first and will not be returned at its normal place.
Killer moves will be played as soon as possible. As Killer moves are stored for the whole ply a Killer move might not be valid for the current position. Therefore we need to wait until they are generated by the phased move generation. Killers will then be pushed to the top of the list of the generation stage.
Evasion is a parameter given when the position is in check and only evasion moves should be generated. For testing purposes this is a parameter for now but obviously we could determine checks very quickly internally in this function. The idea of evasion is to avoid generating moves which are obviously not getting the king out of check. This may reduce the total number of generated moves but there might still be a few non legal moves. This is the case if considering and calculating all possible scenarios is more expensive than to just generate the move and dismiss is later. Because of beta cuts off we quite often will never have to check the full legality of these moves anyway.
func (*Movegen) HasLegalMove ¶
HasLegalMove determines if we have at least one legal move. We only have to find one legal move. We search for any KING, PAWN, KNIGHT, BISHOP, ROOK, QUEEN move and return immediately if we found one. The order of our search is approx from the most likely to the least likely.
func (*Movegen) KillerMoves ¶
func (mg *Movegen) KillerMoves() *[2]Move
KillerMoves returns a pointer to the killer moves array
func (*Movegen) ResetOnDemand ¶
func (mg *Movegen) ResetOnDemand()
ResetOnDemand resets the move on demand generator to start fresh. Also deletes Killer and PV moves.
func (*Movegen) SetHistoryData ¶ added in v1.0.0
SetHistoryData provides a pointer to the search's history data for the move generator so it can optimize sorting.
func (*Movegen) SetPvMove ¶
func (mg *Movegen) SetPvMove(move Move)
SetPvMove sets a PV move which should be returned first by the OnDemand MoveGenerator.
func (*Movegen) StoreKiller ¶
func (mg *Movegen) StoreKiller(move Move)
StoreKiller provides the on demand move generator with a new killer move which should be returned as soon as possible when generating moves with the on demand generator.
type Perft ¶
type Perft struct {
Nodes uint64
CheckCounter uint64
CheckMateCounter uint64
CaptureCounter uint64
EnpassantCounter uint64
CastleCounter uint64
PromotionCounter uint64
// contains filtered or unexported fields
}
Perft is class to test move generation of the chess engine.
func (*Perft) StartPerft ¶
StartPerft is using normal or on demand move generation and doesn't divide the the perft depths. If this has been started in a go routine it can be stopped via Stop()
func (*Perft) StartPerftMulti ¶
StartPerftMulti is using normal or on demand move generation and doesn't divide the the perft depths. It iterates through the given start to end depths. If this has been started in a go routine it can be stopped via Stop()
Source Files