Struct alcibiades::Move

pub struct Move(_);

Represents a move on the chessboard.

Move is a u64 number. It contains 3 types of information:

1. Information about the played move itself.

2. Information needed so as to be able to undo the move and restore the board into the exact same state as before.

3. Move ordering info -- moves with higher move score are tried first.

Bits 0-15 contain the whole information about the move itself. This is called "move digest" and is laid out the following way:

  15                                                           0
 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 | Move  |    Origin square      |   Destination square  | Aux   |
 | type  |       6 bits          |        6 bits         | data  |
 | 2 bits|   |   |   |   |   |   |   |   |   |   |   |   | 2 bits|
 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

There are 4 "move type"s: 0) en-passant capture; 1) pawn promotion; 2) castling; 3) normal move. "Aux data" encodes the type of the promoted piece if the move type is pawn promotion, otherwise it is zero.

Bits 16-31 contain the information needed to undo the move:

  31                                                          16
 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 |   |   |  Captured |  Played   |   Castling    |   En-passant  |
 | 0 | 0 |  piece    |  piece    |    rights     |      file     |
 |   |   |  3 bits   |  3 bits   |    4 bits     |     4 bits    |
 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

If the previous move was a double pawn push, "en-passant file" contains pushed pawn's file (a value between 0 and 7). Otherwise it contains 8. "Castling rights" holds the castling rights before the move was played. When "Captured piece" is stored, its bits are inverted, so that MVV-LVA (Most valuable victim -- least valuable aggressor) move ordering is followed for moves that have the same "score".

Bits 32-63 contain the "score" field, which is used to influence move ordering.

Methods

impl Move

fn new(
    move_type: MoveType,
    orig_square: Square,
    dest_square: Square,
    aux_data: usize,
    captured_piece: PieceType,
    played_piece: PieceType,
    castling_rights: CastlingRights,
    enpassant_file: usize,
    score: u32
) -> Move

Creates a new instance.

fn invalid() -> Move

Creates an invalid move instance.

The returned instance tries to mimic a legal move, but its move digest equals MoveDigest::invalid(). This is sometimes useful in places where any move is required but no is available.

fn piece_from_aux_data(pp_code: usize) -> PieceType

Decodes the promoted piece type from the raw value returned by aux_data.

The interpretation of the raw value is: 0 -- queen, 1 -- rook, 2 -- bishop, 3 -- knight.

fn set_score(&mut self, score: u32)

Assigns a new score for the move.

fn score(&self) -> u32

Returns the assigned move score.

fn move_type(&self) -> MoveType

Returns the move type.

fn played_piece(&self) -> PieceType

Returns the played piece type.

Castling is considered as king's move.

fn orig_square(&self) -> Square

Returns the origin square of the played piece.

fn dest_square(&self) -> Square

Returns the destination square for the played piece.

fn captured_piece(&self) -> PieceType

Returns the captured piece type.

fn enpassant_file(&self) -> usize

If the previous move was a double pawn push, returns pushed pawn's file (a value between 0 and 7). Otherwise returns 8.

fn castling_rights(&self) -> CastlingRights

Returns the castling rights as they were before the move was played.

fn aux_data(&self) -> usize

Returns a value between 0 and 3 representing the auxiliary data.

When the move type is pawn promotion, "aux data" encodes the promoted piece type. For all other move types "aux data" is zero.

fn digest(&self) -> MoveDigest

Returns the least significant 16 bits of the raw move value.

fn notation(&self) -> String

Returns the algebraic notation of the move.

Examples: e2e4, e7e5, e1g1 (white short castling), e7e8q (for promotion).

fn is_pawn_advance_or_capure(&self) -> bool

Returns true if the move is a pawn advance or a capture, false otherwise.

fn is_null(&self) -> bool

Returns if the move is a null move.

"Null move" is a pseudo-move that changes nothing on the board except the side to move. It is sometimes useful to include a speculative null move in the search tree to achieve more aggressive pruning. Null moves are represented as king's moves for which the origin and destination squares are the same.

Trait Implementations

impl Debug for Move

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Clone for Move

fn clone(&self) -> Move

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Move

impl PartialOrd for Move

fn partial_cmp(&self, __arg_0: &Move) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, __arg_0: &Move) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, __arg_0: &Move) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, __arg_0: &Move) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, __arg_0: &Move) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Ord for Move

fn cmp(&self, __arg_0: &Move) -> Ordering

This method returns an Ordering between self and other.

impl PartialEq for Move

fn eq(&self, __arg_0: &Move) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, __arg_0: &Move) -> bool

This method tests for !=.

impl Eq for Move

impl Display for Move

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.