use crate::possible_moves::PossibleMoves;
use crate::{Piece, PieceColor, SquareCoordinate};
#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};
use std::hash::{Hash, Hasher};
#[cfg(test)]
mod tests;
/// A checker board,
/// organized in the following structure:
/// ```txt
/// 11 05 31 25
/// 10 04 30 24
/// 03 29 23 17
/// 02 28 22 16
/// 27 21 15 09
/// 26 20 14 08
/// 19 13 07 01
/// 18 12 06 00
/// ```
#[derive(Copy, Clone, Debug, Eq)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct CheckersBitBoard {
/// If the space contains a piece, it's a 1
pieces: u32,
/// If the piece is black, 1, otherwise 0
color: u32,
/// 1 if the piece is a king
kings: u32,
/// The player who has the next turn
turn: PieceColor,
}
impl Default for CheckersBitBoard {
/// Returns the starting position
fn default() -> Self {
Self::starting_position()
}
}
impl PartialEq for CheckersBitBoard {
fn eq(&self, other: &Self) -> bool {
self.pieces == other.pieces
&& self.pieces & self.color == other.pieces & other.color
&& self.pieces & self.kings == other.pieces & other.kings
&& self.turn == other.turn
}
}
impl Hash for CheckersBitBoard {
/// Hashes with only the pieces part, to ensure correctness and efficiency
fn hash<H: Hasher>(&self, hasher: &mut H) {
self.hash_code().hash(hasher)
}
}
impl CheckersBitBoard {
/// Creates a new Checkers BitBoard
///
/// # Arguments
///
/// * `pieces` - Each bit is 1 if the corresponding space contains a piece
/// * `color` - For each space with a piece, the value is 1 if it's dark, and 0 otherwise.
/// Bits for spaces without colors are undefined
/// * `kings` - For each space with a piece, the value is 1 if it's a king, and 0 otherwise.
/// Bits for spaces without colors are undefined
///
/// # Example
///
/// ```
/// // This is the starting position
/// use model::{CheckersBitBoard, PieceColor};
/// let board = CheckersBitBoard::new(0b11011111101111100111100111100111,
/// 0b00111100001100001100001111001111,
/// 0,
/// PieceColor::Dark);
/// ```
#[must_use]
pub const fn new(pieces: u32, color: u32, kings: u32, turn: PieceColor) -> Self {
Self {
pieces,
color,
kings,
turn,
}
}
/// Creates a board at the starting position
#[must_use]
pub const fn starting_position() -> Self {
const STARTING_BITBOARD: CheckersBitBoard = CheckersBitBoard::new(
0b11100111100111100111110111111011,
0b00001100001111001111001111000011,
0,
PieceColor::Dark,
);
STARTING_BITBOARD
}
#[must_use]
pub const fn hash_code(self) -> u64 {
(((self.color & self.pieces) as u64) << 32) | (((!self.color & self.pieces) as u64) << 32)
}
/// Gets the bits that represent where pieces are on the board
#[must_use]
pub const fn pieces_bits(self) -> u32 {
self.pieces
}
/// Gets the bits that represents the color of each piece on the board
///
/// # Safety
///
/// This is inherently unsafe, because this also returns the bits of empty squares
#[must_use]
pub const fn color_bits(self) -> u32 {
self.color
}
/// Gets the bits that represents the status of each piece on the board
///
/// # Safety
///
/// This is inherently unsafe, because this also returns the bits of empty squares
#[must_use]
pub const fn king_bits(self) -> u32 {
self.kings
}
/// The player whose turn it is
#[must_use]
pub const fn turn(self) -> PieceColor {
self.turn
}
/// Gets the piece at a given row column coordinate
///
/// # Arguments
///
/// * `row` - The row. The a file is row 0
/// * `col` - The column. The first rank is column 0
#[must_use]
// TODO test
pub fn get_at_row_col(self, row: usize, col: usize) -> Option<Piece> {
if row > 32 || col > 32 {
None
} else {
let value = SquareCoordinate::new(row as u8, col as u8).to_value();
if let Some(value) = value {
if self.piece_at(value) {
Some(Piece::new(
unsafe { self.king_at_unchecked(value) },
unsafe { self.color_at_unchecked(value) },
))
} else {
None
}
} else {
None
}
}
}
/// Checks if there's a piece at the given space value
///
/// # Arguments
///
/// * `value` - The value of the space to check
///
/// # Example
///
/// ```
/// use model::CheckersBitBoard;
/// let board = CheckersBitBoard::default();
/// match board.piece_at(0) {
/// true => println!("There's a piece in the bottom right"),
/// false => println!("The bottom right is empty")
/// }
/// ```
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
#[must_use]
pub const fn piece_at(self, value: usize) -> bool {
((self.pieces >> value) & 1) == 1
}
/// Checks the color at the piece in the given location,
/// without checking if there's a piece there
///
/// # Arguments
///
/// * `value` - The value of the space to check
///
/// # Example
///
/// ```
/// use model::CheckersBitBoard;
/// use model::PieceColor;
/// let board = CheckersBitBoard::default();
/// if board.piece_at(0) {
/// match unsafe {board.color_at_unchecked(0)} {
/// PieceColor::Dark => println!("The piece in the bottom right is dark colored"),
/// PieceColor::Light => println!("The piece in the bottom right is light colored")
/// }
/// }
/// ```
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Checking the color at a square that is empty results in undefined behavior
#[must_use]
pub const unsafe fn color_at_unchecked(self, value: usize) -> PieceColor {
if ((self.color >> value) & 1) != 0 {
PieceColor::Dark
} else {
PieceColor::Light
}
}
/// Checks the color at the piece in the given location.
/// Returns `None` if there isn't a piece there
///
/// # Arguments
///
/// * `value` - The value of the space to check
///
/// # Example
///
/// ```
/// use model::CheckersBitBoard;
/// use model::PieceColor;
/// let board = CheckersBitBoard::default();
/// if let Some(color) = board.color_at(0) {
/// match color {
/// PieceColor::Dark => println!("The piece in the bottom right is dark colored"),
/// PieceColor::Light => println!("The piece in the bottom left is light colored")
/// }
/// }
/// ```
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
#[must_use]
pub const fn color_at(self, value: usize) -> Option<PieceColor> {
if self.piece_at(value) {
// safety: if this block runs, then it's already confirmed a piece exists here
Some(unsafe { self.color_at_unchecked(value) })
} else {
None
}
}
/// Checks if the given location has a king, without checking if there's a piece there
///
/// # Arguments
///
/// * `value` - The value of the space to check
///
/// # Example
///
/// ```
/// use model::CheckersBitBoard;
/// let board = CheckersBitBoard::default();
/// if board.piece_at(0) {
/// match unsafe {board.king_at_unchecked(0)} {
/// true => println!("The piece in the bottom right is a king"),
/// false => println!("The piece in the bottom right is a peasant")
/// }
/// }
/// ```
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Checking a square that is empty results in undefined behavior
#[must_use]
pub const unsafe fn king_at_unchecked(self, value: usize) -> bool {
((self.kings >> value) & 1) == 1
}
/// Checks if the piece in the given location is a king.
/// Returns `None` if there isn't a piece there
///
/// # Arguments
///
/// * `value` - The value of the space to check
///
/// # Example
///
/// ```
/// use model::CheckersBitBoard;
/// let board = CheckersBitBoard::default();
/// if let Some(status) = board.king_at(0) {
/// match status {
/// true => println!("The piece in the bottom right is a king"),
/// false => println!("The piece in the bottom right is a peasant")
/// }
/// }
/// ```
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
#[must_use]
pub const fn king_at(self, value: usize) -> Option<bool> {
if self.piece_at(value) {
// safety: if this block runs, then it's already confirmed a piece exists here
Some(unsafe { self.king_at_unchecked(value) })
} else {
None
}
}
/// Change whose turn it is, without modifying the board
#[must_use]
// TODO test
pub const fn flip_turn(self) -> Self {
CheckersBitBoard::new(self.pieces, self.color, self.kings, self.turn.flip())
}
/// Moves a piece from `start` to `dest`. The original location will be empty.
/// This does not mutate the original board.
/// If a piece already exists at `dest`, it will be overwritten.
///
/// # Arguments
///
/// * `start` - The original location of the piece
/// * `dest` - The new location
///
/// # Panics
///
/// Panics if `start` or `dest` is greater than or equal to 32
///
/// # Safety
///
/// Results in undefined behavior if `start` does not contain a piece
// TODO rip out so we don't need to check for both black and white promotion
#[must_use]
pub const unsafe fn move_piece_to_unchecked(self, start: usize, dest: usize) -> Self {
// Clears the bit at the starting value
// Sets the bit at the destination value
let pieces = (self.pieces & !(1 << start)) | (1 << dest);
// Clears the bit at the destination value
// Sets the value at the destination to the value of the start
let color = (self.color & !(1 << dest)) | (((self.color >> start) & 1) << dest);
// The squares where certain pieces should be promoted
const DARK_PROMOTION_MASK: u32 = 0b10000010000000000000100000100000;
const LIGHT_PROMOTION_MASK: u32 = 0b1000001000001000001;
// Clears the bit at the destination value
// Sets the value at the destination to the value of the start
// Promotes if the end of the board was reached
let kings = (self.kings & !(1 << dest))
| (((self.kings >> start) & 1) << dest)
| (color & DARK_PROMOTION_MASK)
| (!color & LIGHT_PROMOTION_MASK);
let turn = self.turn.flip();
CheckersBitBoard::new(pieces, color, kings, turn)
}
/// Moves a piece from `value` to `(value + amount) % 32`. The original location will be empty.
/// This does not mutate the original board
///
/// # Arguments
///
/// * `value` - The original location of the piece
/// * `amount` - The amount to shift the location by
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32,
/// or `value + amount` is greater than `usize::MAX`
///
/// # Safety
///
/// This results in undefined behavior if `value` does not contain a piece
#[must_use]
const unsafe fn move_piece_forward_unchecked(self, value: usize, amount: usize) -> Self {
self.move_piece_to_unchecked(value, (value + amount) & 31)
}
/// Moves a piece from `value` to `(value - amount) % 32`. The original location will be empty.
/// This does not mutate the original board.
/// If a piece already exists there, then it will be overwritten
///
/// # Arguments
///
/// * `value` - The original location of the piece
/// * `amount` - The amount to shift the location by
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// This results in undefined behavior if `value` does not contain a piece
#[must_use]
const unsafe fn move_piece_backward_unchecked(self, value: usize, amount: usize) -> Self {
self.move_piece_to_unchecked(value, value.wrapping_sub(amount) & 31)
}
/// Tries to move the piece forward and to the left, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the left side of the board results in undefined behavior.
/// Moving from the top of the board results in undefined behavior.
/// A `value` which doesn't contain a piece results in undefined behavior.
#[must_use]
pub const unsafe fn move_piece_forward_left_unchecked(self, value: usize) -> Self {
self.move_piece_forward_unchecked(value, 7)
}
/// Tries to move the piece forward and to the right, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the right side of the board results in undefined behavior.
/// Moving from the top of the board results in undefined behavior.
/// A `value` which doesn't contain a piece results in undefined behavior.
#[must_use]
pub const unsafe fn move_piece_forward_right_unchecked(self, value: usize) -> Self {
self.move_piece_forward_unchecked(value, 1)
}
/// Tries to move the piece backward and to the left, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the left side of the board results in undefined behavior.
/// Moving from the bottom of the board results in undefined behavior.
/// A `value` which doesn't contain a piece results in undefined behavior.
#[must_use]
pub const unsafe fn move_piece_backward_left_unchecked(self, value: usize) -> Self {
self.move_piece_backward_unchecked(value, 1)
}
/// Tries to move the piece backward and to the right, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the right side of the board results in undefined behavior.
/// Moving from the bottom of the board results in undefined behavior.
/// A `value` which doesn't contain a piece results in undefined behavior.
#[must_use]
pub const unsafe fn move_piece_backward_right_unchecked(self, value: usize) -> Self {
self.move_piece_backward_unchecked(value, 7)
}
/// Clears a space on the board. If the space is empty, then this function does nothing.
///
/// # Arguments
///
/// * `value` - The value of the space to clear
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
#[must_use]
pub const fn clear_piece(self, value: usize) -> Self {
let pieces = self.pieces & !(1 << value);
CheckersBitBoard::new(pieces, self.color, self.kings, self.turn)
}
/// Tries to jump the piece forward and to the left, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten.
/// The space the piece jumps over is cleared
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the left side of the board results in undefined behavior.
/// Moving from the top of the board results in undefined behavior
#[must_use]
// TODO test the edge cases of the below if statement
pub const unsafe fn jump_piece_forward_left_unchecked(self, value: usize) -> Self {
let is_king = self.king_at_unchecked(value);
let board = self
.move_piece_forward_unchecked(value, 14)
.clear_piece((value + 7) & 31);
const KING_MASK: u32 = 0b00100000100000100000000000001000;
if (is_king || (((1 << value) & KING_MASK) == 0))
&& PossibleMoves::has_jumps_at(board.flip_turn(), (value + 14) & 31)
{
board.flip_turn()
} else {
board
}
}
/// Tries to move the piece forward and to the right, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
/// The space the piece jumps over is cleared
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the right side of the board results in undefined behavior.
/// Moving from the top of the board results in undefined behavior
#[must_use]
pub const unsafe fn jump_piece_forward_right_unchecked(self, value: usize) -> Self {
let is_king = self.king_at_unchecked(value);
let board = self
.move_piece_forward_unchecked(value, 2)
.clear_piece((value + 1) & 31);
const KING_MASK: u32 = 0b00100000100000100000000000001000;
if (is_king || (((1 << value) & KING_MASK) == 0))
&& PossibleMoves::has_jumps_at(board.flip_turn(), (value + 2) & 31)
{
board.flip_turn()
} else {
board
}
}
/// Tries to move the piece backward and to the left, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
/// The space the piece jumps over is cleared
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the left side of the board results in undefined behavior.
/// Moving from the bottom of the board results in undefined behavior
#[must_use]
pub const unsafe fn jump_piece_backward_left_unchecked(self, value: usize) -> Self {
let is_king = self.king_at_unchecked(value);
let board = self
.move_piece_backward_unchecked(value, 2)
.clear_piece(value.wrapping_sub(1) & 31);
const KING_MASK: u32 = 0b00000100000100000100000100000000;
if (is_king || (((1 << value) & KING_MASK) == 0))
&& PossibleMoves::has_jumps_at(board.flip_turn(), value.wrapping_sub(2) & 31)
{
board.flip_turn()
} else {
board
}
}
/// Tries to move the piece backward and to the right, without checking if it's a legal move.
/// If a piece already exists there, then it will be overwritten
/// The space the piece jumps over is cleared
///
/// # Arguments
///
/// * `value` - The original location of the piece
///
/// # Panics
///
/// Panics if `value` is greater than or equal to 32
///
/// # Safety
///
/// Moving from the right side of the board results in undefined behavior.
/// Moving from the bottom of the board results in undefined behavior
#[must_use]
pub const unsafe fn jump_piece_backward_right_unchecked(self, value: usize) -> Self {
let is_king = self.king_at_unchecked(value);
let board = self
.move_piece_backward_unchecked(value, 14)
.clear_piece(value.wrapping_sub(7) & 31);
const KING_MASK: u32 = 0b00000100000100000100000100000000;
if (is_king || (((1 << value) & KING_MASK) == 0))
&& PossibleMoves::has_jumps_at(board.flip_turn(), value.wrapping_sub(14) & 31)
{
board.flip_turn()
} else {
board
}
}
}
|
