/ 
Chess-Plisco-0.4
River stage zero No dependents
/ Chess::Plisco

NAME

Chess::Plisco - A comprehensive chess library for Perl

SYNOPSIS

use Chess::Plisco(:all);

$pos = Chess::Plisco->new;
$pos = Chess::Plisco->new('k7/8/8/8/8/8/8/7K w - - 0 1');

DESCRIPTION

Chess::Plisco is a comprehensive chess library for Perl, aiming at being as fast and efficient as possible for a scripting language. It is also somewhat opinionated but this is not an end in itself but owed to its intention of being fast and efficient. In doubt, flexibility is sacrificed for performance and efficiency.

The library features:

bitboards for board representation
macros/inline functions for often used computations
legality checks for moves
magic bitboards for generation of sliding piece moves and attacks
handling of moves in Standard-Algebraic Notation (SAN) as well as coordinate notation
FEN (Forsyth-Edwards Notation) import and export
EPD (Extended Position Notation) parser
Static Exchange Evaluation (SEE)
Zobrist Keys

For a gentler introduction, please see Chess::Plisco::Tutorial. The rest of this document contains reference documentation only.

If performance is key for you, you are strongly advised to have a look at Chess::Plisco::Macro which documents macros resp. inline functions that speed up tasks that can be done with Chess::Plisco significantly.

The class exports a number of constants that can either be imported individually, by export tag, or all at once by the export tag ':all'. All constants are prefixed with 'CP_' and you will have little reason to not import all constants.

Internals

An instance of a Chess::Plisco is a blessed array reference. You can access its properties through accessor macros or by using constants for the array indices.

A move in Chess::Plisco is a regular scalar, more precisely an unsigned integer. You can access its properties with the move methods described below.

It is guaranteed that every legal chess move is represented by a non-zero integer. It is therefore safe to use moves in boolean context.

Terminology

For the sake of brevity, this document uses the following terms without further explanation:

Square

A square is a square of the chess board as a string like "e4" or "f7".

Coordinates

Coordinates are a pair of a file (0-7) and a rank (0-7).

Shift

A "shift" is an integer in the range of 0-63 where 0 is the shift for "a1" and 63 is the shift for "h8".

Bitboard

A bitboard is an unsigned 64-bit integer. Each bit stands for one square of the chess board.

Mask

A mask is a bitboard with exactly one bit set. The mask representing "e4" is a 1 shifted left 28 bits, because the shift for "e4" is 28.

Move

When an argument is called "move", it is really an integer representing a chess move.

Notation

When an argument is called "notation", it is a supported notation of a chess move, either Standard-Algebraic Notation SAN or coordinate notation.

Limitations

Chess::Plisco requires 64-bit support for Perl. It will not run on 32-bit Perls.

Similar Software

Chess::Rep and Chess::Play provide similar functionality. Both compile a lot faster than Chess::Plisco but once compiled, a perft test of Chess::Plisco runs more than 30 times faster than one of Chess::Play and more than 100 times faster than one of Chess::Rep.

At the time of this writing, Chess::Plisco also outperforms python-chess by about 50 %.

CONSTRUCTORS

new([FEN])

Creates a new Chess::Plisco instance that represents the starting position of standard chess.

If an argument is passed to the constructor, it is interpreted as a position in Forsyth-Edwards Notation (FEN). This has the same effect as using the constructor newFromFEN.

newFromFEN(FEN)

Creates a new Chess::Plisco instance from a string containing the Forsyth-Edwards Notation (FEN) of a chess position. The only difference to new() is that the string argument is required.

This constructor may throw an exception if the described position does not meet the requirements of the library.

All legal chess positions meet the requirements of the library. But positions that are not legal and may cause the library to malfunction, are rejected.

copy(POSITION)

Clones POSITION.

OVERLOADED OPERATORS

In string context, the position is encoded in Forsyth-Edwards Notation. No other operators are overloaded.

Note that the Forsyth-Edwards Notation does not cover all aspects of a chess position, especially the history of moves. String-wise equality of two instances of a Chess::Plisco does therefore not imply that the two positions are identical. Use the method "equal" for a strict equality check.

METHODS

General Methods

toFEN

Renders the position to Forsyth-Edwards Notation. Alternatively, you can just use the object as a string:

$position = Chess::Plisco->new;
say $position->toFEN;
say "$position"; # Does the same as above.
legalMoves

Returns a list of legal moves for the current position. A move is just an integer.

pseudoLegalMoves

Generates all pseudo-legal moves for the current position.

Pseudo-legal are all moves that can be executed by the pieces on the side to move ignoring whether the side to move is in check after the move.

Only the lower 15 bits of the move are set, that means the start and destination square, and a possible promotion piece.

If you also need the captured piece and the color, you either have to call "legalMoves" or you must use the state information returned from "doMove" to retrieve the enriched move. The first element of the state array is the enriched move.

pseudoLegalAttacks

Like "pseudoLegalMoves" but only returns "interesting" moves. Interesting moves are captures, promotions, and moves directly giving check. Discovered checks are not generated. This has performance reasons.

You will want to call this method for generating moves in a quiescence search. Since quiescence search is imperfect anyway, it is assumed that ignoring discovered checks does not have a negative impact.

Future versions of this library may include discovered checks.

moveNumbers

Class method that returns an array of all theoretically possible moves in standard chess. These move numbers have the following structure:

color (1 bit): Either "CP_BLACK" or "CP_WHITE".
capture (3 bits): The captured piece if any, one of "CP_NONE", "CP_PAWN", "CP_KNIGHT", "CP_BISHOP", "CP_ROOK", "CP_QUEEN", or (!) "CP_KING", see below.
mover (3 bits): The piece that move, one of "CP_PAWN", "CP_KNIGHT", "CP_BISHOP", "CP_ROOK", "CP_QUEEN", or <L/CP_KING>.
promote (3 bits): The piece that is promoted to if any, one of "CP_KNIGHT", "CP_BISHOP", "CP_ROOK", or "CP_QUEEN".
from (6 bits): The starting square of the piece as a bit shift. In case of castling, this is the king's starting square.
to (6 bits): The destination square of the piece as a bit shift. In case of castling, this is the king's destination square.

If the captured piece is encoded as a king, it is really a pawn that gets captured en passant.

The size of this array is 45356, see this document at the chess programming wiki.

equals(POSITION)

Returns true if the current position is equivalent to POSITION.

Methods for Accessing Position Properties

whitePieces

Returns the bitboard of all white pieces.

blackPieces

Returns the bitboard of all black pieces.

occupied

Returns the bitboard of all squares that are occupied by any piece.

vacant

Returns the bitboard of all squares that are not occupied by any piece.

kings

Returns the bitboard of all kings (black and white).

queens

Returns the bitboard of all queens (black and white).

rooks

Returns the bitboard of all rooks (black and white).

bishops

Returns the bitboard of all bishops (black and white).

knights

Returns the bitboard of all knights (black and white).

pawns

Returns the bitboard of all pawns (black and white).

toMove

Returns the side to move, either "CP_BLACK" or "CP_WHITE".

halfMoves

Returns the number of half-moves made. Initially, this is 0. After white has made their first move, it is 1. After black has made their first move, it is 2, and so on.

reversibleClock

Returns the number of reversible moves immediately leading to the current position. The following moves are irreversible:

Pawn moves

Reason: A pawn cannot move backwards.

Captures

Reason: Captured pieces are gone for good.

First king move of each side

Reason: The side to move loses the castling rights.

First move of each rook of each side

Reason: The side to move loses at least one of their castling rights.

Castlings

Reason: The side to move loses the castling rights. This is also implied by the fact that they are necessarily the first king move.

The half-move-clock is important because both players can claim a draw, when the half-move clock has reached 50.

halfMoveClock

Like "irreversibleClock" but only captures and pawn moves are considered irreversible. Changes to the castling state are ignored. This is the value that is relevant for claiming a draw according to the 50-move Rule.

signature

Returns a 64-bit Zobrist key (aka 64-bit integer) that identifies the position. Properties taken into account are:

piece positions
color to move
castling rights
en-passant status

Note that hash collisions albeit unlikely, may occur because 64 bit are, of course, not sufficient to uniquely identify a chess position.

The signature computed for a certain position is guaranteed not to change for one release of Chess::Plisco. In order to compute different signatures, you have to override either the pseudo-random number generator "RNG" or its seed "CP_RANDOM_SEED". If you turn the constant "CP_RANDOM_SEED" into a non-constant subroutine, you can also get different signatures, whenever you re-load the library.

inCheck

Returns false if the side to move is not in check, a truthy value otherwise. The truthy value returned is a bitboard of all pieces giving check.

evasion

If the side to move is in check, returns the required check evasion strategy:

"CP_EVASION_KING_MOVE"

The king must move. This is the case, when multiple pieces give check.

"CP_EVASION_CAPTURE"

Either the king must move or the piece giving check must be captured.

"CP_EVASION_ALL"

Either the king must move, the piece giving check must be captured, or another piece must be moved between the king and the attacking piece.

evasionSquares

If a check can be evaded by moving a piece between the king and the attacking piece of the opponent, this bitboard gives all squares where the check can be blocked. These are all squares between the king and the attacking piece, including the square where the attacker is standing.

enPassantShift

If en-passant is possible, returns the shift of the square where the capturing pawn has to move. If en-passant is not possible, 0 is returned. 0 happens to be the shift of "a1" but "a1" is not a valid en-passant square. It is therefore safe to use this method in boolean context.

material

Gives the material balance from the perspective of the white player. That means that all white pieces have a positive value, and all black pieces have a negative value.

The values are:

"CP_QUEEN_VALUE" for each queen
"CP_ROOK_VALUE" for each rook
"CP_BISHOP_VALUE" for each bishop
"CP_KNIGHT_VALUE" for each knight
"CP_PAWN_VALUE" for each pawn

These constants can be overridden by inheriting from Chess::Plisco.

Note: Kings do not count!

whiteKingSideCastlingRight

Returns a truthy value if white still has the right to castle king-side ("O-O"), false otherwise.

whiteQueenSideCastlingRight

Returns a truthy value if white still has the right to castle queen-side, ("O-O-O"), false otherwise.

blackKingSideCastlingRight

Returns a truthy value if black still has the right to castle king-side ("O-O"), false otherwise.

blackQueenSideCastlingRight

Returns a truthy value if black still has the right to castle queen-side, ("O-O-O"), false otherwise.

castlingRights

Returns a bitmap of castling rights for the current position:

0x1 is set if white can still castle king-side
0x2 is set if white can still castle queen-side
0x4 is set if black can still castle king-side
0x8 is set if black can still castle queen-side
kingShift

Return the shift of the square of the king of the side to move. This information is needed internally.

info

Returns an integer encoding various other aspects of the position. You do not need this because there are dedicated methods available for all these properties.

Move Methods

parseMove(NOTATION)

Parses the string NOTATION into an integer representing the move or returns false, if the NOTATION cannot be parsed or is an illegal move.

NOTATION can either be a move in Standard Algebraic Notation (SAN) or in coordinate notation. Coordinate notation is the format used by most chess engines and is the concatenation of the start and destination square and a possible promotion piece, for example "e2e4" or "f2f1q".

SAN(MOVE)

Renders the integer MOVE into Standard-Algebraic Notation SAN, for example "e4", "Bxc4", "O-O", or "fxe1=Q".

moveCoordinateNotation(MOVE)

Renders the integer MOVE into coordinate notation, for example "e2e4" or "f2f1q".

LAN(MOVE)

Returns the Long Algebraic Notation LAN of the move. This is an alias for "moveCoordinateNotation".

moveEquivalent(MOVE1, MOVE2)

Returns true if the significant parts of MOVE1 and MOVE2 are equivalent. This is the case, when the start and destination square, and a possible promotion piece are equal.

Note that the piece that moves is not significant because it can be retrieved from the position. Nevertheless, the piece that moves is set by the methods "pseudoLegalMoves" and "pseudoLegalAttacks" on the moves returned. If you store a best move in a transposition table make sure to keep that in mind, when you compare moves.

Although, this is technically a class method you should keep in mind that the redundant parts of the moves depend on the current position.

moveSignificant(MOVE)

Returns MOVE with all insignificant bits stripped off. See "moveEquivalent" for what is considered significant.

Although, this is technically a class method you should keep in mind that the redundant parts of the moves depend on the current position.

moveFrom(MOVE)

Extracts the shift (0-63) of the starting square.

moveSetFrom(MOVE, FROM)

Sets the shift (0-63) of the starting square in MOVE to FROM and returns the move.

moveTo(MOVE)

Extracts the shift (0-63) of the destination square.

moveSetTo(MOVE, TO)

Sets the shift (0-63) of the destination square in MOVE to TO and returns the move.

movePromote(MOVE)

Extracts the piece that a pawn is promoted to if the move is a promotion. Returns either "CP_QUEEN", "CP_ROOK", "CP_BISHOP", or "CP_KNIGHT".

moveSetPromote(MOVE, PROMOTE)

Sets the piece to promote to in MOVE to PROMOTE and returns the move. The piece should be one of "CP_QUEEN", "CP_ROOK", "CP_BISHOP", or "CP_KNIGHT".

movePiece(MOVE)

Extracts the piece that does the move. Returns one of "CP_KING", "CP_QUEEN", "CP_ROOK", "CP_BISHOP", "CP_KNIGHT", or "CP_PAWN".

moveSetPiece(MOVE, PIECE)

Sets the piece that moves in MOVE to PIECE and returns the move. The piece should be one of "CP_KING", "CP_QUEEN", "CP_ROOK", "CP_BISHOP", "CP_KNIGHT", or "CP_PAWN".

moveCaptured(MOVE)

Extracts the piece that gets captured if any. Returns one of "CP_QUEEN", "CP_ROOK", "CP_BISHOP", "CP_KNIGHT", "CP_PAWN", "CP_NO_PIECE".

moveSetCaptured(MOVE, PIECE)

Sets the piece that gets captured in MOVE to PIECE and returns the move. The piece should be one of "CP_QUEEN", "CP_ROOK", "CP_BISHOP", "CP_KNIGHT", "CP_PAWN", "CP_NO_PIECE".

moveColor(MOVE)

Extracts the color that does the move.

moveSetColor(MOVE, COLOR)

Sets the color in MOVE to COLOR and returns the move.

moveLegal(MOVE|NOTATION)

Returns a truthy value, when the argument is a valid and legal move. The move can be given either as an integer returned by "parseMove" or as a string that is accepted by "parseMove".

applyMove(MOVE|NOTATION)

Parses the move given in NOTATION and applies it to the position if the move is valid and legal. Otherwise false is returned. You can also pass the move as an integer as returned by "parseMove".

The method returns state information that can later be used to undo the move and reset the position to the state it had before the move was applied.

Engines should use the method "doMove" instead because it is faster.

unapplyMove(STATE)

If STATE is state information returned by "applyMove", takes back the move that was given as an argument to "applyMove".

Engines should use the method "undoMove" instead because it is faster.

doMove(MOVE)

Applies the move represented by the integer(!) MOVE to the position. If the move is legal, the method returns state information that can be used to undo the move with "undoMove".

The method returns false, if the move is illegal. Note that this is not a complete legality check but works only for those moves that "pseudoLegalMoves" has returned for the current position.

This method is fast and is the one that should be used by engines.

The state information returned is an array of various bits of information. The first one is the move itself but the captured piece is set in that move.

undoMove(STATE)

If STATE is state information returned by "doMove", takes back the move that was given as an argument to "doMove".

This method is fast and is the one that should be used by engines.

SEE(MOVE)

Does a static exchange evaluation SEE for move MOVE. MOVE must be a capture, a promotion, a move giving check, or any combination of it. It returns the raw material balance expected from the move.

The routine assumes, that after MOVE had been made, all moves that re-capture on the target field of MOVE will be executed, starting with the least valuable attacker of each side proceeding to the most valuable attacker. As soon as a re-capture becomes disadvantageous, the sequence stops, and the balance up to that point is returned.

Disadvantageous means that advancing to the "next round" would make the result worse. For example a bishop would not normally capture a pawn that is protected.

If you assign different values to bishops and knights by overriding "CP_KNIGHT_VALUE" and "CP_BISHOP_VALUE" you may receive small values by this routine, if the exchange of bishops and knights is involved. Depending on your preferences you may ignore absolute values under a certain threshold, for example 100 centipawns.

It should also be noted that the routine assumes that the values of pieces follows this relation:

pawn < knight <= bishop < rook < queen (< king)

Methods for Converting Locations

squareToShift(SQUARE)

Converts SQUARE to a shift.

This is a class method.

squareToCoordinates(SQUARE)

Converts SQUARE to coordinates. It returns a list, not a an array reference. Be sure to call it in array context!

This is a class method.

shiftToSquare(SHIFT)

Converts SHIFT to a square.

This is a class method.

shiftToCoordinates(SHIFT)

Converts a shift to coordinates. It returns a list, not a an array reference. Be sure to call it in array context!

This is a class method.

coordinatesToSquare(FILE, RANK)

Converts coordinates to a square.

This is a class method.

coordinatesToShift(FILE, RANK)

Converts coordinates to a shift.

This is a class method.

Methods for Inspecting a Square

The following methods answer the question which piece of which color occupies a particular location on the chess board.

pieceAtSquare(SQUARE)

In array context returns a pair of a piece and a color. In scalar context, only the piece is returned. The piece is one of "CP_PAWN", "CP_KNIGHT", "CP_BISHOP", "CP_ROOK", "CP_QUEEN", "CP_KING", or "CP_NO_PIECE" if the square is empty.

The color is one of "CP_BLACK" or "CP_WHITE". If the square is empty, undef is returned instead of a color.

This method is relatively expensive!

pieceAtCoordinates(FILE, RANK)

In array context returns a pair of a piece and a color. In scalar context, only the piece is returned. The piece is one of "CP_PAWN", "CP_KNIGHT", "CP_BISHOP", "CP_ROOK", "CP_QUEEN", "CP_KING", or "CP_NO_PIECE" if the square is empty.

The color is one of "CP_BLACK" or "CP_WHITE". If the square is empty, undef is returned instead of a color.

This method is relatively expensive!

pieceAtShift(SHIFT)

In array context returns a pair of a piece and a color. In scalar context, only the piece is returned. The piece is one of "CP_PAWN", "CP_KNIGHT", "CP_BISHOP", "CP_ROOK", "CP_QUEEN", "CP_KING", or "CP_NO_PIECE" if the square is empty.

The color is one of "CP_BLACK" or "CP_WHITE". If the square is empty, undef is returned instead of a color.

This method is relatively expensive!

Analysis Methods

These methods can be used to analyze features of the current position.

insufficientMaterial

Returns true if none of the two sides has sufficient material to win, false otherwise.

This is not a general-purpose draw detection but only checks the material of both sides. If one side has at least a pawn, rook, or queen, the material is sufficient to mate. A mate is also possible when both sides have at least one minor piece with the exception of king and bishop vs king and bishop. This can only be won if the two bishops move on differently colored squares.

One minor piece against a lone king is always a draw.

attacked(SHIFT)

Returns true if the square indicated by SHIFT is attacked by a piece of the opponent.

moveAttacked(MOVE|NOTATION)

Returns true if when executing MOVE, the moving piece would be attacked by a piece of the opponent. A typical usage example would be to check if the king moving from FROM to TO would move into check.

You can give the move either as an integer or in one of the supported move notations.

movePinned(MOVE|NOTATION)

Returns true if a piece doing MOVE is pinned. A piece is pinned if it would leave the king in check when doing the move. Exposing other pieces to an opponent attack is not considered a pin by this method.

You can give the move either as an integer or in one of the supported move notations.

rMagic(SHIFT, OCCUPANCY)

Returns a bitboard of all squares that a rook can reach from SHIFT. OCCUPANCY is a bitboard of all squares that are occupied by pieces. The first piece that the sliding piece would reach is considered a potential captured of a capture and is a valid target square.

See "Understanding rMagic and bMagic" in Chess::Plisco::Tutorial for more information.

bMagic(SHIFT, OCCUPANCY)

Returns a bitboard of all squares that a bishop can reach from SHIFT. OCCUPANCY is a bitboard of all squares that are occupied by pieces. The first piece that the sliding piece would reach is considered a potential captured of a capture and is a valid target square.

See "Understanding rMagic and bMagic" in Chess::Plisco::Tutorial for more information.

Bit(board) Fiddling Methods

bitboardPopcount(BITBOARD)

Counts and returns the bits sets in BITBOARD.

This does the same as the builtin function __builtin_popcountll of the C compilers llvm and gcc.

bitboardClearLeastSet(BITBOARD)

Clears the least signicant bit that is set in BITBOARD.

bitboardClearButLeastSet(BITBOARD)

Clears all set bits in BITBOARD except for the least significant one that is set.

bitboardCountTrailingZbits(BITBOARD)

Counts all trailing zero bits, that is all bits that are not set starting with the least significant bit (bit number 0).

bitboardCountIsolatedTrailingZbits(BITBOARD)

Counts all trailing zero bits, that is all bits that are not set starting with the least significant bit (bit number 0). In other words, this method gives you the shift of the set bit in BITBOARD. It only works if exactlye one bit is set in BITBOARD, otherwise the behavior is undefined.

This does the same as the builtin function __builtin_ctzll of the C compilers llvm and gcc.

bitboardMoreThanOneSet(BITBOARD)

Returns a truthy value if more than one bit in BITBOARD is set, false otherwise.

Perft Methods

A "perft" (PERFormance Test) is a standard test for measuring the performance of the move generator. Starting from the current position, it generates all legal moves up to the specified depth. It is also important for testing the correct functioning of the move generator because the number of leave nodes for certain positions are well known.

Internally, each legal move is applied to the position, then the next level is computed from the resulting position, and finally the move is undone.

perftByCopy(POSITION, DEPTH)

Does a performance test for position POSITION to depth DEPTH. Returns the number of leaf nodes found.

Instead of calling "undoMove" the moves found are applied to a copy of the current position that is discarded later. This is currently slightly faster than undoing the move programatically with "undoMove".

Note that you have to pass a Chess::Plisco instance as the first argument even when calling it as an instance method! This has performance reason.

perftByUndo(DEPTH)

Does a performance test for the current position to depth DEPTH. Returns the number of leaf nodes found.

Moves are undone programmatically with "undoMove". This is currently slightly slower than just copying the position, see "perftByCopy".

perftByCopyWithOutput(DEPTH, FILEHANDLE)

Does the the same as perftByCopy but prints out all top-level moves found with the number of subnodes for each move. The time needed is measured with "gettimeofday" in Time::HiRes and reported at the end as well as the number of nodes found.

This method can be used directly to implement the command "go perft" for a UCI compatible chess engine.

perftByUndoWithOutput(DEPTH, FILEHANDLE)

Does the the same as perftByUndo but prints out all top-level moves found with the number of subnodes for each move. The time needed is measured with "gettimeofday" in Time::HiRes and reported at the end as well as the number of nodes found.

This method can be used directly to implement the command "go perft" for a UCI compatible chess engine.

Methods for Debugging and Diagnostics

consistent

Does an extensive consistency check on the position and throws an exception if any inconsistency is encountered.

dumpBitboard(BITBOARD)

Generate a string representation of BITBOARD in ASCII art.

dumpAll

Generates a string representation of all bitboards in ASCII art plus some additional information.

dumpInfo(INFO)

Returns a string with the decoded position information as retured by "info".

movesCoordinateNotation(MOVES)

Takes an array of moves (as integers) and converts it into an array of moves in coordinate notation.

Other Methods

RNG

Returns a pseudo-random integer created by the well-known xor-shift pseudo-random number generator.

The random-number generator is always seeded with the same seed (initial value). This is on purpose, so that the numbers returned are deterministic. The method is currently only used for generating the Zobrist keys for position signatures.

If you want a different seed, you should override the constant "CP_RANDOM_SEED".

PROPERTIES

You can access individual properties either by using index constants or by using accessor macros from Chess::Plisco::Macro. All accessor macros can be assigned to; they are L-values. But you are strongly advised to modify properties of a Chess::Plisco instance only with the methods documented here.

For getting or setting the bitboard of all white pieces, you have these options:

$whites_pieces = $pos->[CP_W_PIECES];
$white_pieces = cp_w_pieces $pos;
$white_pieces = cp_w_pieces($pos);
$pos->[CP_W_PIECES] = $white_pieces;
cp_w_pieces $pos = $white_pieces;
cp_w_pieces($pos) = $white_pieces;

The macros (all starting with "cp_") are only available when you have loaded Chess::Plisco::Macro, see there for more information.

All elements of the position array are documented below under "Accessor Indexes (:accessors)".

EXPORT TAGS

The module exports only constants, all prefixed with "CP_".

Note that (lowercase) macros "cp_" are defined by using Chess::Plisco::Macro.

All Constants (:all)

You can import all constants with the export tag ":all".

Accessor Indexes (:accessors)

The array indices were carefully so that the following conditions are met:

All piece types ("CP_PAWN", "CP_KNIGHT", ..., "CP_KING") can be used as indexes into the instance in order to retrieve their respective bitboard
The white bitboard comes directly before the black bitboard.

The bitboard for the pieces of the side to move is therefore always at the location CP_POS_WHITE_PIECES + $pos-toMove>. Or in other words, the constants CP_POS_PAWNS and CP_PAWN (likewise for the other piece types) are guaranteed to be the same and to point to the corresponding piece bitboard.

POS->[CP_POS_WHITE_PIECES]

A bitboard of all white pieces on the board. See also "whitePieces".

POS->[CP_POS_BLACK_PIECES]

A bitboard of all black pieces on the board. See also "blackPieces".

POS->[CP_POS_KINGS]

A bitboard of all kings (black and white) on the board. See also "kings".

POS->[CP_POS_QUEENS]

A bitboard of all rooks (black and white) on the board. See also "queens".

POS->[CP_POS_ROOKS]

A bitboard of all rooks (black and white) on the board. See also "rooks".

POS->[CP_POS_BISHOPS]

A bitboard of all bishops (black and white) on the board. See also "bishops".

POS->[CP_POS_KNIGHTS]

A bitboard of all knights (black and white) on the board. See also "knights".

POS->[CP_POS_PAWNS]

A bitboard of all pawns (black and white) on the board. See also "pawns".

POS->[CP_POS_HALF_MOVES]

The number of half-moves made. See also "halfMoves".

POS->[CP_POS_HALF_MOVE_CLOCK]

The current value of the half-move clock. See also "halfMoveClock".

POS->[CP_POS_IRREVERSIBLE_CLOCK]

The current value of the irreversible clock. See also "irreversibleClock".

POS->[CP_POS_IN_CHECK]

Bitmask of pieces giving check. See also "inCheck".

POS->[CP_POS_EVASION_SQUARES]

Bitboard of squares where a check can be blocked. See also "evasionSquares".

POS->[CP_POS_SIGNATURE]

Same as "signature".

POS->[CP_POS_INFO]

Additional properties of the position. See also "info".

Piece Constants (:pieces)

CP_WHITE => 0

Symbolic constant for white pieces, side to move, and so on.

CP_BLACK => 1

Symbolic constant for black pieces, side to move, and so on. Actually, usage of this constant is avoided internally so that any truthy value can be used. Most of the time, this is simply the else branch of a conditional.

CP_NO_PIECE => 0

Symbolic constant for no piece.

CP_PAWN

Symbolic constant for a pawn.

CP_KNIGHT

Symbolic constant for a knight.

CP_BISHOP

Symbolic constant for a bishop.

CP_ROOK

Symbolic constant for a rook.

CP_QUEEN

Symbolic constant for a queen.

CP_KING

Symbolic constant for a king.

CP_PAWN_VALUE => 100

Value of a pawn in centipawns. Feel free to override this constant in derived classes.

CP_KNIGHT_VALUE => 300

Value of a knight in centipawns. Feel free to override this constant in derived classes.

CP_BISHOP_VALUE => 300

Value of a bishop in centipawns. Feel free to override this constant in derived classes.

CP_ROOK_VALUE => 500

Value of a rook in centipawns. Feel free to override this constant in derived classes.

CP_QUEEN_VALUE => 900

Value of a queen in centipawns. Feel free to override this constant in derived classes.

Note that there is no value for a king. This is on purpose.

CP_PIECE_CHARS

An array of arrays that maps numeric piece constants (CP_PAWN, CP_KNIGHT, ...) to characters. The first array are uppercase letters, normally used for white pieces, the second one are lowercase letters, normally used for black pieces.

Example to get the character for a black knight:

$char = CP_PIECE_CHARS->[CP_BLACK]->[CP_KNIGHT];

Board Constants (:board)

CP_A_MASK .. CP_H_MASK

These are bitboards of all files ("a" to "h") of the chess board.

CP_1_MASK .. CP_8_MASK

These are bitboards of all ranks ("1" to "8") of the chess board.

CP_WHITE_MASK

Bitboard of all white squares (b1, d1, ... g8)

CP_BLACK_MASK

Bitboard of all black squares (a1, c1, ... h8)

CP_FILE_A .. CP_FILE_H

0-based numbers of all files ("a" to "h").

CP_RANK_1 .. CP_RANK_8

0-based numbers of all ranks ("1" to "8").

CP_A1 .. CP_H8

Shifts for all squares of the chess board.

Magic Moves Resp. Magic Bitboard Constants (:magicmoves)

These are all large data tables that are used internally for the magic bitboards that generate the attack masks for the sliding pieces (queens, bishops, and rooks). See the source if you are curious. Otherwise just import them if you want to use the macros cp_mm_bmagic() and cp_mm_rmagic() from Chess::Plisco::Macro.

CP_MAGICMOVES_B_MAGICS

Internal.

CP_MAGICMOVES_R_MAGICS

Internal.

CP_MAGICMOVES_B_MASK

Internal.

CP_MAGICMOVES_R_MASK

Internal.

CP_MAGICMOVESBDB

Internal.

CP_MAGICMOVESRDB

Internal.

Auxiliary Constants (:aux)

CP_INT_SIZE

The size in bits of an integer. Should be at least 64.

CP_CHAR_BITS

The number of bits in a char. Should be 8.

CP_RANDOM_SEED

A pretty arbitrary value used to initialize the pseudo-random number generator "RNG".

COPYRIGHT

Copyright (C) 2021 Guido Flohr <guido.flohr@cantanea.com>.

SEE ALSO

Chess::Plisco::Macro, perl(1)