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GNU AFFERO GENERAL PUBLIC LICENSE
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# This file is automatically @generated by Cargo.
# It is not intended for manual editing.
version = 4
[[package]]
name = "eschac"
version = "0.1.0"

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[package]
name = "eschac"
version = "0.1.0"
edition = "2021"
authors = ["Paul-Nicolas Madelaine <pnm@pnm.tf>"]
license = "AGPL-3.0-or-later"
description = "computing chess moves"
repository = "https://git.pnm.tf/pnm/eschac"
keywords = ["chess"]
[profile.dev]
opt-level = 3

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# eschac
A library for computing chess moves.
## Overview
eschac implements fast legal move generation and a copy-make interface that enforces at compile
time that no illegal move is played, with no runtime checks and no potential panics.
## Example
```rust
use eschac::prelude::*;
// read a position from a text record
let setup = "7k/4P1rp/5Q2/5p2/1Pp1bP2/8/r4K1P/6R1 w - -".parse::<Setup>()?;
let position = setup.validate()?;
// read a move in algebraic notation
let san = "Ke1".parse::<San>()?;
let m = san.to_move(&position)?;
// play the move (note the absence of error handling)
let position = m.make();
// generate all the legal moves on the new position
let moves = position.legal_moves();
for m in moves {
// print the UCI notation of each move
println!("{}", m.to_uci());
}
```
## Comparison with [shakmaty](https://crates.io/crates/shakmaty)
shakmaty is another Rust library for chess processing. It is written by Niklas Fiekas, whose work
greatly inspired the development of eschac. For most purposes, shakmaty is probably a better
option, as eschac comes short of its miriad of features.
Both libraries have the same core features:
- vocabulary to describe the chessboard (squares, pieces, etc.)
- parsing and editing positions
- parsing standard move notations
- fast legal move generation and play
**eschac** distinguishes itself with:
- a focus on performance
- a more compact board representation
- its use of the borrow checker to guarantee only legal moves are played
**shakmaty** will be more suitable for a lot of applications, with:
- vocabulary to describe and work with games, not just positions
- insufficient material detection
- PGN parsing
- Zobrist hashing
- Syzygy endgame tablebases
- chess960 and other variants
- etc.
## License
eschac is licensed under [AGPL-3.0](./COPYING) (or any later version at your option).

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use std::iter::ExactSizeIterator;
use std::iter::FusedIterator;
use std::mem::MaybeUninit;
#[derive(Clone)]
pub(crate) struct ArrayVec<T: Copy, const N: usize> {
len: usize,
array: [MaybeUninit<T>; N],
}
impl<T: Copy, const N: usize> ArrayVec<T, N> {
#[inline]
pub(crate) fn new() -> Self {
Self {
len: 0,
array: [const { MaybeUninit::uninit() }; N],
}
}
#[inline]
pub(crate) unsafe fn push_unchecked(&mut self, m: T) {
debug_assert!(self.len < N);
unsafe {
self.array.get_unchecked_mut(self.len).write(m);
self.len = self.len.unchecked_add(1);
}
}
#[inline]
pub(crate) fn len(&self) -> usize {
self.len
}
#[inline]
pub(crate) fn get(&self, index: usize) -> Option<&T> {
if index < self.len {
Some(unsafe { self.array.as_slice().get_unchecked(index).assume_init_ref() })
} else {
None
}
}
#[inline]
pub(crate) fn as_slice_mut(&mut self) -> &mut [T] {
unsafe { std::mem::transmute::<_, &mut [T]>(self.array.get_unchecked_mut(0..self.len)) }
}
}
impl<'l, T: Copy, const N: usize> IntoIterator for &'l ArrayVec<T, N> {
type Item = T;
type IntoIter = ArrayVecIter<'l, T, N>;
#[inline]
fn into_iter(self) -> Self::IntoIter {
ArrayVecIter {
array: self,
index: 0,
}
}
}
pub(crate) struct ArrayVecIter<'l, T: Copy, const N: usize> {
array: &'l ArrayVec<T, N>,
index: usize,
}
impl<'l, T: Copy, const N: usize> Iterator for ArrayVecIter<'l, T, N> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
if self.index < self.array.len {
unsafe {
let item = self
.array
.array
.get_unchecked(self.index)
.assume_init_read();
self.index = self.index.unchecked_add(1);
Some(item)
}
} else {
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.len();
(len, Some(len))
}
}
impl<'l, T: Copy, const N: usize> FusedIterator for ArrayVecIter<'l, T, N> {}
impl<'l, T: Copy, const N: usize> ExactSizeIterator for ArrayVecIter<'l, T, N> {
#[inline]
fn len(&self) -> usize {
unsafe { self.array.len().unchecked_sub(self.index) }
}
}
impl<T: Copy, const N: usize> IntoIterator for ArrayVec<T, N> {
type Item = T;
type IntoIter = ArrayVecIntoIter<T, N>;
#[inline]
fn into_iter(self) -> Self::IntoIter {
ArrayVecIntoIter {
array: self,
index: 0,
}
}
}
pub(crate) struct ArrayVecIntoIter<T: Copy, const N: usize> {
array: ArrayVec<T, N>,
index: usize,
}
impl<T: Copy, const N: usize> Iterator for ArrayVecIntoIter<T, N> {
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
if self.index < self.array.len {
unsafe {
let item = self
.array
.array
.get_unchecked(self.index)
.assume_init_read();
self.index = self.index.unchecked_add(1);
Some(item)
}
} else {
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.len();
(len, Some(len))
}
}
impl<T: Copy, const N: usize> FusedIterator for ArrayVecIntoIter<T, N> {}
impl<T: Copy, const N: usize> ExactSizeIterator for ArrayVecIntoIter<T, N> {
#[inline]
fn len(&self) -> usize {
unsafe { self.array.len().unchecked_sub(self.index) }
}
}

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use crate::board::*;
use std::iter::ExactSizeIterator;
use std::iter::FusedIterator;
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Bitboard(pub(crate) u64);
impl Bitboard {
#[inline]
pub fn new() -> Self {
Self(0)
}
#[inline]
pub fn is_empty(&self) -> bool {
self.0 == 0
}
#[inline]
pub fn first(&self) -> Option<Square> {
let mask = self.0;
match mask {
0 => None,
_ => Some(unsafe { Square::transmute(mask.trailing_zeros() as u8) }),
}
}
#[inline]
pub fn pop(&mut self) -> Option<Square> {
let Self(ref mut mask) = self;
let square = match mask {
0 => None,
_ => Some(unsafe { Square::transmute(mask.trailing_zeros() as u8) }),
};
*mask &= mask.wrapping_sub(1);
square
}
#[inline]
pub fn insert(&mut self, square: Square) {
self.0 |= 1 << square as u8;
}
#[inline]
pub fn trans(&self, direction: Direction) -> Self {
match direction {
Direction::North => Self(self.0 << 8),
Direction::NorthEast => Self(self.0 << 9) & !File::A.bitboard(),
Direction::East => Self(self.0 << 1) & !File::A.bitboard(),
Direction::SouthEast => Self(self.0 >> 7) & !File::A.bitboard(),
Direction::South => Self(self.0 >> 8),
Direction::SouthWest => Self(self.0 >> 9) & !File::H.bitboard(),
Direction::West => Self(self.0 >> 1) & !File::H.bitboard(),
Direction::NorthWest => Self(self.0 << 7) & !File::H.bitboard(),
}
}
#[inline]
pub fn contains(&self, square: Square) -> bool {
self.0 & (1 << square as u8) != 0
}
#[inline]
pub fn mirror(self) -> Bitboard {
let [a, b, c, d, e, f, g, h] = self.0.to_le_bytes();
Self(u64::from_le_bytes([h, g, f, e, d, c, b, a]))
}
}
impl std::ops::BitOr for Bitboard {
type Output = Self;
#[inline]
fn bitor(self, rhs: Self) -> Self::Output {
Self(self.0 | rhs.0)
}
}
impl std::ops::BitAnd for Bitboard {
type Output = Self;
#[inline]
fn bitand(self, rhs: Self) -> Self::Output {
Self(self.0 & rhs.0)
}
}
impl std::ops::BitXor for Bitboard {
type Output = Self;
#[inline]
fn bitxor(self, rhs: Self) -> Self::Output {
Self(self.0 ^ rhs.0)
}
}
impl std::ops::BitOrAssign for Bitboard {
#[inline]
fn bitor_assign(&mut self, rhs: Self) {
self.0 |= rhs.0;
}
}
impl std::ops::BitAndAssign for Bitboard {
#[inline]
fn bitand_assign(&mut self, rhs: Self) {
self.0 &= rhs.0;
}
}
impl std::ops::BitXorAssign for Bitboard {
#[inline]
fn bitxor_assign(&mut self, rhs: Self) {
self.0 ^= rhs.0;
}
}
impl std::ops::Not for Bitboard {
type Output = Self;
#[inline]
fn not(self) -> Self::Output {
Self(!self.0)
}
}
impl Iterator for Bitboard {
type Item = Square;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
self.pop()
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.len();
(len, Some(len))
}
#[inline]
fn for_each<F>(self, mut f: F)
where
Self: Sized,
F: FnMut(Self::Item),
{
let mut mask = self.0;
while mask != 0 {
f(unsafe { Square::transmute(mask.trailing_zeros() as u8) });
mask &= mask.wrapping_sub(1);
}
}
#[inline]
fn fold<B, F>(self, init: B, mut f: F) -> B
where
Self: Sized,
F: FnMut(B, Self::Item) -> B,
{
let mut mask = self.0;
let mut acc = init;
while mask != 0 {
acc = f(acc, unsafe {
Square::transmute(mask.trailing_zeros() as u8)
});
mask &= mask.wrapping_sub(1);
}
acc
}
}
impl FusedIterator for Bitboard {}
impl ExactSizeIterator for Bitboard {
#[inline]
fn len(&self) -> usize {
self.0.count_ones() as usize
}
}
pub(crate) trait BitboardIterExt {
fn reduce_or(self) -> Bitboard;
}
impl<T> BitboardIterExt for T
where
T: Iterator<Item = Bitboard>,
{
#[inline]
fn reduce_or(self) -> Bitboard {
self.fold(Bitboard(0), |a, b| a | b)
}
}

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//! Chessboard vocabulary.
use crate::bitboard::*;
macro_rules! container {
($a:ident, $b:ident, $n:literal) => {
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub(crate) struct $b<T>(pub(crate) [T; $n]);
#[allow(unused)]
impl<T> $b<T> {
#[inline]
pub fn new<F>(f: F) -> Self
where
F: FnMut($a) -> T,
{
Self($a::all().map(f))
}
#[inline]
pub fn get(&self, k: $a) -> &T {
unsafe { self.0.get_unchecked(k as usize) }
}
#[inline]
pub fn get_mut(&mut self, k: $a) -> &mut T {
unsafe { self.0.get_unchecked_mut(k as usize) }
}
}
};
}
/// The players.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
pub enum Color {
White,
Black,
}
container!(Color, ByColor, 2);
impl Color {
#[inline]
pub fn all() -> [Self; 2] {
[Self::White, Self::Black]
}
#[inline]
pub(crate) fn home_rank(self) -> Rank {
match self {
Self::White => Rank::First,
Self::Black => Rank::Eighth,
}
}
#[inline]
pub(crate) fn promotion_rank(self) -> Rank {
match self {
Self::White => Rank::Eighth,
Self::Black => Rank::First,
}
}
#[inline]
pub(crate) fn forward(self) -> Direction {
match self {
Self::White => Direction::North,
Self::Black => Direction::South,
}
}
}
impl std::ops::Not for Color {
type Output = Self;
#[inline]
fn not(self) -> Self::Output {
match self {
Self::Black => Self::White,
Self::White => Self::Black,
}
}
}
/// A column of the board.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
pub enum File {
A,
B,
C,
D,
E,
F,
G,
H,
}
container!(File, ByFile, 8);
impl File {
#[inline]
pub fn all() -> [Self; 8] {
[
Self::A,
Self::B,
Self::C,
Self::D,
Self::E,
Self::F,
Self::G,
Self::H,
]
}
#[inline]
pub fn to_char(self) -> char {
self.to_ascii() as char
}
#[inline]
pub fn from_char(c: char) -> Option<Self> {
Self::from_ascii(c as u8)
}
#[inline]
pub(crate) fn to_ascii(self) -> u8 {
self as u8 + b'a'
}
#[inline]
pub(crate) fn from_ascii(c: u8) -> Option<Self> {
(c <= b'h')
.then(|| c.checked_sub(b'a').map(|i| unsafe { Self::transmute(i) }))
.flatten()
}
#[inline]
pub(crate) fn bitboard(self) -> Bitboard {
Bitboard(0x0101010101010101 << (self as u8))
}
#[inline]
pub(crate) unsafe fn transmute(value: u8) -> Self {
debug_assert!(value < 8);
std::mem::transmute(value)
}
}
impl std::fmt::Display for File {
#[inline]
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "{}", self.to_char())
}
}
/// A row of the board.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
pub enum Rank {
First,
Second,
Third,
Fourth,
Fifth,
Sixth,
Seventh,
Eighth,
}
container!(Rank, ByRank, 8);
impl Rank {
#[inline]
pub fn all() -> [Self; 8] {
[
Self::First,
Self::Second,
Self::Third,
Self::Fourth,
Self::Fifth,
Self::Sixth,
Self::Seventh,
Self::Eighth,
]
}
#[inline]
pub fn to_char(self) -> char {
self.to_ascii() as char
}
#[inline]
pub fn from_char(c: char) -> Option<Self> {
Self::from_ascii(c as u8)
}
#[inline]
pub fn mirror(self) -> Self {
unsafe { Self::transmute(7_u8.unchecked_sub(self as u8)) }
}
#[inline]
pub(crate) fn to_ascii(self) -> u8 {
self as u8 + b'1'
}
#[inline]
pub(crate) fn from_ascii(c: u8) -> Option<Self> {
(c <= b'8')
.then(|| c.checked_sub(b'1').map(|i| unsafe { Self::transmute(i) }))
.flatten()
}
#[inline]
pub(crate) fn bitboard(self) -> Bitboard {
Bitboard(0xFF << ((self as u64) << 3))
}
#[inline]
pub(crate) unsafe fn transmute(value: u8) -> Self {
debug_assert!(value < 8);
std::mem::transmute(value)
}
}
impl std::fmt::Display for Rank {
#[inline]
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "{}", self.to_char())
}
}
/// A square of the board.
#[rustfmt::skip]
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
pub enum Square{
A1, B1, C1, D1, E1, F1, G1, H1,
A2, B2, C2, D2, E2, F2, G2, H2,
A3, B3, C3, D3, E3, F3, G3, H3,
A4, B4, C4, D4, E4, F4, G4, H4,
A5, B5, C5, D5, E5, F5, G5, H5,
A6, B6, C6, D6, E6, F6, G6, H6,
A7, B7, C7, D7, E7, F7, G7, H7,
A8, B8, C8, D8, E8, F8, G8, H8,
}
container!(Square, BySquare, 64);
impl Square {
#[inline]
#[rustfmt::skip]
pub fn all() -> [Self; 64] {
[
Self::A1, Self::B1, Self::C1, Self::D1, Self::E1, Self::F1, Self::G1, Self::H1,
Self::A2, Self::B2, Self::C2, Self::D2, Self::E2, Self::F2, Self::G2, Self::H2,
Self::A3, Self::B3, Self::C3, Self::D3, Self::E3, Self::F3, Self::G3, Self::H3,
Self::A4, Self::B4, Self::C4, Self::D4, Self::E4, Self::F4, Self::G4, Self::H4,
Self::A5, Self::B5, Self::C5, Self::D5, Self::E5, Self::F5, Self::G5, Self::H5,
Self::A6, Self::B6, Self::C6, Self::D6, Self::E6, Self::F6, Self::G6, Self::H6,
Self::A7, Self::B7, Self::C7, Self::D7, Self::E7, Self::F7, Self::G7, Self::H7,
Self::A8, Self::B8, Self::C8, Self::D8, Self::E8, Self::F8, Self::G8, Self::H8,
]
}
#[inline]
pub fn new(file: File, rank: Rank) -> Self {
unsafe { Self::transmute(((rank as u8) << 3) + file as u8) }
}
#[inline]
pub fn file(self) -> File {
unsafe { File::transmute((self as u8) & 7) }
}
#[inline]
pub fn rank(self) -> Rank {
unsafe { Rank::transmute((self as u8) >> 3) }
}
#[inline]
pub fn mirror(self) -> Self {
Self::new(self.file(), self.rank().mirror())
}
#[inline]
pub(crate) fn bitboard(self) -> Bitboard {
Bitboard(1 << self as u8)
}
#[inline]
#[rustfmt::skip]
pub(crate) fn to_str(self) -> &'static str {
match self {
Self::A1 => "a1", Self::B1 => "b1", Self::C1 => "c1", Self::D1 => "d1", Self::E1 => "e1", Self::F1 => "f1", Self::G1 => "g1", Self::H1 => "h1",
Self::A2 => "a2", Self::B2 => "b2", Self::C2 => "c2", Self::D2 => "d2", Self::E2 => "e2", Self::F2 => "f2", Self::G2 => "g2", Self::H2 => "h2",
Self::A3 => "a3", Self::B3 => "b3", Self::C3 => "c3", Self::D3 => "d3", Self::E3 => "e3", Self::F3 => "f3", Self::G3 => "g3", Self::H3 => "h3",
Self::A4 => "a4", Self::B4 => "b4", Self::C4 => "c4", Self::D4 => "d4", Self::E4 => "e4", Self::F4 => "f4", Self::G4 => "g4", Self::H4 => "h4",
Self::A5 => "a5", Self::B5 => "b5", Self::C5 => "c5", Self::D5 => "d5", Self::E5 => "e5", Self::F5 => "f5", Self::G5 => "g5", Self::H5 => "h5",
Self::A6 => "a6", Self::B6 => "b6", Self::C6 => "c6", Self::D6 => "d6", Self::E6 => "e6", Self::F6 => "f6", Self::G6 => "g6", Self::H6 => "h6",
Self::A7 => "a7", Self::B7 => "b7", Self::C7 => "c7", Self::D7 => "d7", Self::E7 => "e7", Self::F7 => "f7", Self::G7 => "g7", Self::H7 => "h7",
Self::A8 => "a8", Self::B8 => "b8", Self::C8 => "c8", Self::D8 => "d8", Self::E8 => "e8", Self::F8 => "f8", Self::G8 => "g8", Self::H8 => "h8",
}
}
#[inline]
pub(crate) fn from_str(s: &str) -> Option<Self> {
match s.as_bytes() {
[f, r] => Self::from_ascii(&[*f, *r]),
_ => None,
}
}
#[inline]
pub(crate) fn from_ascii(s: &[u8; 2]) -> Option<Self> {
let [f, r] = *s;
Some(Self::new(File::from_ascii(f)?, Rank::from_ascii(r)?))
}
#[inline]
pub(crate) fn trans(self, direction: Direction) -> Option<Self> {
self.check_trans(direction).then(|| unsafe {
// SAFETY: condition is checked before doing the translation
self.trans_unchecked(direction)
})
}
/// SAFETY: the translation must not move the square outside the board
#[inline]
pub(crate) unsafe fn trans_unchecked(self, direction: Direction) -> Self {
debug_assert!(self.check_trans(direction));
let i = self as u8;
unsafe {
Self::transmute(match direction {
Direction::East => i.unchecked_add(1),
Direction::NorthEast => i.unchecked_add(9),
Direction::North => i.unchecked_add(8),
Direction::NorthWest => i.unchecked_add(7),
Direction::SouthEast => i.unchecked_sub(7),
Direction::South => i.unchecked_sub(8),
Direction::SouthWest => i.unchecked_sub(9),
Direction::West => i.unchecked_sub(1),
})
}
}
/// Returns `false` if the translation would move the square outside the board
#[inline]
fn check_trans(self, direction: Direction) -> bool {
match direction {
Direction::East => self.file() < File::H,
Direction::NorthEast => self.file() < File::H && self.rank() < Rank::Eighth,
Direction::North => self.rank() < Rank::Eighth,
Direction::NorthWest => self.file() > File::A && self.rank() < Rank::Eighth,
Direction::SouthEast => self.file() < File::H && self.rank() > Rank::First,
Direction::South => self.rank() > Rank::First,
Direction::SouthWest => self.file() > File::A && self.rank() > Rank::First,
Direction::West => self.file() > File::A,
}
}
#[inline]
pub(crate) unsafe fn transmute(value: u8) -> Self {
debug_assert!(value < 64);
std::mem::transmute(value)
}
}
impl std::fmt::Display for Square {
#[inline]
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
f.write_str(self.to_str())
}
}
/// An error while parsing a [`Square`].
#[derive(Debug)]
pub struct ParseSquareError;
impl std::fmt::Display for ParseSquareError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str("invalid square syntax")
}
}
impl std::error::Error for ParseSquareError {}
impl std::str::FromStr for Square {
type Err = ParseSquareError;
#[inline]
fn from_str(s: &str) -> Result<Self, Self::Err> {
Self::from_str(s).ok_or(ParseSquareError)
}
}
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
#[rustfmt::skip]
pub(crate) enum OptionSquare {
_A1, _B1, _C1, _D1, _E1, _F1, _G1, _H1,
_A2, _B2, _C2, _D2, _E2, _F2, _G2, _H2,
_A3, _B3, _C3, _D3, _E3, _F3, _G3, _H3,
_A4, _B4, _C4, _D4, _E4, _F4, _G4, _H4,
_A5, _B5, _C5, _D5, _E5, _F5, _G5, _H5,
_A6, _B6, _C6, _D6, _E6, _F6, _G6, _H6,
_A7, _B7, _C7, _D7, _E7, _F7, _G7, _H7,
_A8, _B8, _C8, _D8, _E8, _F8, _G8, _H8,
None,
}
impl OptionSquare {
#[inline]
pub(crate) fn new(square: Option<Square>) -> OptionSquare {
match square {
Some(square) => Self::from_square(square),
None => Self::None,
}
}
#[inline]
pub(crate) fn try_into_square(self) -> Option<Square> {
unsafe {
match self {
Self::None => None,
_ => Some(Square::transmute(self as u8)),
}
}
}
#[inline]
pub(crate) fn from_square(square: Square) -> Self {
unsafe { std::mem::transmute(square) }
}
}
/// A type of piece.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
pub enum Role {
Pawn = 1,
Knight,
Bishop,
Rook,
Queen,
King,
}
impl Role {
#[inline]
pub fn all() -> [Self; 6] {
[
Self::Pawn,
Self::Knight,
Self::Bishop,
Self::Rook,
Self::Queen,
Self::King,
]
}
#[inline]
pub(crate) fn to_char_uppercase(self) -> char {
match self {
Self::Pawn => 'P',
Self::Knight => 'N',
Self::Bishop => 'B',
Self::Rook => 'R',
Self::Queen => 'Q',
Self::King => 'K',
}
}
#[inline]
pub(crate) fn to_char_lowercase(self) -> char {
match self {
Self::Pawn => 'p',
Self::Knight => 'n',
Self::Bishop => 'b',
Self::Rook => 'r',
Self::Queen => 'q',
Self::King => 'k',
}
}
#[inline]
pub(crate) fn from_ascii(x: u8) -> Option<Self> {
Some(match x {
b'p' | b'P' => Self::Pawn,
b'n' | b'N' => Self::Knight,
b'b' | b'B' => Self::Bishop,
b'r' | b'R' => Self::Rook,
b'q' | b'Q' => Self::Queen,
b'k' | b'K' => Self::King,
_ => return None,
})
}
#[inline]
pub(crate) unsafe fn transmute(i: u8) -> Self {
debug_assert!(i > 0 && i <= 6, "got {i}");
unsafe { std::mem::transmute(i) }
}
}
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub(crate) struct ByRole<T>(pub(crate) [T; 6]);
#[allow(unused)]
impl<T> ByRole<T> {
#[inline]
pub fn new<F>(f: F) -> Self
where
F: FnMut(Role) -> T,
{
Self(Role::all().map(f))
}
#[inline]
pub fn get(&self, kind: Role) -> &T {
unsafe { self.0.get_unchecked((kind as usize).unchecked_sub(1)) }
}
#[inline]
pub fn get_mut(&mut self, kind: Role) -> &mut T {
unsafe { self.0.get_unchecked_mut((kind as usize).unchecked_sub(1)) }
}
}
impl<T> ByRole<T>
where
T: Copy,
{
#[inline]
pub(crate) fn pawn(&self) -> T {
*self.get(Role::Pawn)
}
#[inline]
pub(crate) fn knight(&self) -> T {
*self.get(Role::Knight)
}
#[inline]
pub(crate) fn bishop(&self) -> T {
*self.get(Role::Bishop)
}
#[inline]
pub(crate) fn rook(&self) -> T {
*self.get(Role::Rook)
}
#[inline]
pub(crate) fn queen(&self) -> T {
*self.get(Role::Queen)
}
#[inline]
pub(crate) fn king(&self) -> T {
*self.get(Role::King)
}
}
/// A chess piece (i.e. its [`Role`] and [`Color`]).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Piece {
pub role: Role,
pub color: Color,
}
#[derive(Clone, Copy)]
#[repr(u8)]
pub(crate) enum Direction {
East,
NorthEast,
North,
NorthWest,
SouthEast,
South,
SouthWest,
West,
}
container!(Direction, ByDirection, 8);
impl Direction {
#[inline]
pub fn all() -> [Self; 8] {
[
Self::East,
Self::NorthEast,
Self::North,
Self::NorthWest,
Self::SouthEast,
Self::South,
Self::SouthWest,
Self::West,
]
}
#[inline]
unsafe fn transmute(value: u8) -> Self {
debug_assert!(value < 8);
std::mem::transmute(value)
}
}
impl std::ops::Not for Direction {
type Output = Self;
#[inline]
fn not(self) -> Self::Output {
unsafe { Self::transmute(self as u8 ^ 0b111) }
}
}
/// A side of the board.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(u8)]
pub enum CastlingSide {
/// King's side
Short,
/// Queen's side
Long,
}
container!(CastlingSide, ByCastlingSide, 2);
impl CastlingSide {
#[inline]
pub fn all() -> [Self; 2] {
[Self::Short, Self::Long]
}
#[inline]
pub(crate) fn rook_origin_file(self) -> File {
match self {
Self::Short => File::H,
Self::Long => File::A,
}
}
}
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub(crate) struct CastlingRights(u8);
impl CastlingRights {
#[inline]
pub(crate) fn new() -> Self {
Self(0)
}
#[inline]
pub(crate) const fn full() -> Self {
Self(15)
}
#[inline]
pub(crate) fn get(&self, color: Color, side: CastlingSide) -> bool {
(self.0 & Self::mask(color, side)) != 0
}
#[inline]
pub(crate) fn set(&mut self, color: Color, side: CastlingSide) {
self.0 |= Self::mask(color, side);
}
#[inline]
pub(crate) fn unset(&mut self, color: Color, side: CastlingSide) {
self.0 &= !Self::mask(color, side);
}
#[inline]
pub(crate) fn mirror(&self) -> Self {
Self(((self.0 & 3) << 2) | (self.0 >> 2))
}
#[inline]
const fn mask(color: Color, side: CastlingSide) -> u8 {
match (color, side) {
(Color::White, CastlingSide::Short) => 1,
(Color::White, CastlingSide::Long) => 2,
(Color::Black, CastlingSide::Short) => 4,
(Color::Black, CastlingSide::Long) => 8,
}
}
}

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//! # eschac - a library for computing chess moves
//!
//! eschac implements fast legal move generation and a copy-make interface that enforces at compile
//! time that no illegal move is played, with no runtime checks and no potential panics.
//!
//! ## Overview
//!
//! The most important type in eschac is [`Position`](position::Position), it represents a chess
//! position from which legal moves are generated. [`Position::new`](position::Position::new)
//! returns the starting position of a chess game, and arbitrary positions can be built using the
//! [`Setup`](setup::Setup) type, but they must be validated and converted to a
//! [`Position`](position::Position) to generate moves as eschac does not handle certain illegal --
//! as in unreachable in a normal game -- positions (see
//! [`IllegalPositionReason`](setup::IllegalPositionReason) to know more). Legal moves are then
//! generated using the [`Position::legal_moves`](position::Position::legal_moves) method or
//! obtained from chess notation like [`UciMove`](uci::UciMove) or [`San`](san::San). Moves are
//! represented with the [`Move<'l>`](position::Move) type, which holds a reference to the origin
//! position (hence the lifetime), this ensures the move is played on the correct position.
//! Finally, moves are played using the [`Move::make`](position::Move) method which returns a new
//! [`Position`](position::Position), and on it goes.
//!
//! ## Example
//!
//! ```
//! # (|| -> Result<(), Box<dyn std::error::Error>> {
//!
//! use eschac::prelude::*;
//!
//! // read a position from a text record
//! let setup = "7k/4P1rp/5Q2/5p2/1Pp1bP2/8/r4K1P/6R1 w - -".parse::<Setup>()?;
//! let position = setup.validate()?;
//!
//! // read a move in algebraic notation
//! let san = "Ke1".parse::<San>()?;
//! let m = san.to_move(&position)?;
//!
//! // play the move (note the absence of error handling)
//! let position = m.make();
//!
//! // generate all the legal moves on the new position
//! let moves = position.legal_moves();
//! for m in moves {
//! // print the UCI notation of each move
//! println!("{}", m.to_uci());
//! }
//! # Ok(()) });
//! ```
//!
//! ## Comparison with [shakmaty](https://crates.io/crates/shakmaty)
//!
//! shakmaty is another Rust library for chess processing. It is written by Niklas Fiekas, whose
//! work greatly inspired the development of eschac. For most purposes, shakmaty is probably a
//! better option, as eschac comes short of its miriad of features.
//!
//! Both libraries have the same core features:
//! - vocabulary to describe the chessboard (squares, pieces, etc.)
//! - parsing and editing positions
//! - parsing standard move notations
//! - fast legal move generation and play
//!
//! **eschac** distinguishes itself with:
//! - a focus on performance
//! - a more compact board representation
//! - its use of the borrow checker to guarantee only legal moves are played
//!
//! **shakmaty** will be more suitable for a lot of applications, with:
//! - vocabulary to describe and work with games, not just positions
//! - insufficient material detection
//! - PGN parsing
//! - Zobrist hashing
//! - Syzygy endgame tablebases
//! - chess960 and other variants
//! - etc.
pub(crate) mod array_vec;
pub(crate) mod bitboard;
pub(crate) mod magics;
pub(crate) mod rays;
pub mod board;
pub mod lookup;
pub mod position;
pub mod san;
pub mod setup;
pub mod uci;
/// The eschac prelude.
pub mod prelude {
pub use crate::{position::Position, san::San, setup::Setup, uci::UciMove};
}

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//! Lookup tables initialisation.
//!
//! Move generation in eschac requires about 1MB of precomputed lookup tables.
use crate::bitboard::*;
use crate::board::*;
use crate::magics::*;
use crate::rays::*;
pub(crate) use init::InitialisedLookup;
/// Forces the initialisation of the lookup tables.
///
/// It is not necessary to call this function, as lookup tables are initialised lazily, but it can
/// be used to ensure that they are initialised before a given time.
pub fn init() {
InitialisedLookup::init();
}
pub(crate) struct Lookup {
rays: Rays,
lines: BySquare<BySquare<Bitboard>>,
segments: BySquare<BySquare<Bitboard>>,
pawn_attacks: ByColor<BySquare<Bitboard>>,
king_moves: BySquare<Bitboard>,
knight_moves: BySquare<Bitboard>,
pub(crate) magics: Magics,
}
impl Lookup {
#[inline]
pub(crate) fn line(&self, a: Square, b: Square) -> Bitboard {
*self.lines.get(a).get(b)
}
#[inline]
pub(crate) fn segment(&self, a: Square, b: Square) -> Bitboard {
*self.segments.get(a).get(b)
}
#[inline]
pub(crate) fn ray(&self, square: Square, direction: Direction) -> Bitboard {
self.rays.ray(square, direction)
}
#[inline]
pub(crate) fn king(&self, square: Square) -> Bitboard {
*self.king_moves.get(square)
}
#[inline]
pub(crate) fn knight(&self, square: Square) -> Bitboard {
*self.knight_moves.get(square)
}
#[inline]
pub(crate) fn pawn_attack(&self, color: Color, square: Square) -> Bitboard {
*self.pawn_attacks.get(color).get(square)
}
#[inline]
pub(crate) fn bishop(&self, square: Square, blockers: Bitboard) -> Bitboard {
self.magics.bishop(square, blockers)
}
#[inline]
pub(crate) fn rook(&self, square: Square, blockers: Bitboard) -> Bitboard {
self.magics.rook(square, blockers)
}
/// `role != Pawn`
#[inline]
pub(crate) fn targets(&self, role: Role, from: Square, blockers: Bitboard) -> Bitboard {
match role {
Role::Pawn => unreachable!(),
Role::Knight => self.knight(from),
Role::Bishop => self.bishop(from, blockers),
Role::Rook => self.rook(from, blockers),
Role::Queen => self.bishop(from, blockers) | self.rook(from, blockers),
Role::King => self.king(from),
}
}
pub(crate) fn compute() -> Self {
let rays = Rays::new();
let lines = BySquare::new(|a| {
BySquare::new(|b| {
for d in Direction::all() {
let r = rays.ray(a, d);
if r.contains(b) {
return r;
}
}
Bitboard::new()
})
});
let segments = BySquare::new(|a| {
BySquare::new(|b| {
for d in Direction::all() {
let r = rays.ray(a, d);
if r.contains(b) {
return r & !rays.ray(b, d);
}
}
b.bitboard()
})
});
let pawn_attacks = ByColor::new(|color| {
let direction = match color {
Color::White => Direction::North,
Color::Black => Direction::South,
};
BySquare::new(|square| {
let mut res = Bitboard::new();
if let Some(square) = square.trans(direction) {
square.trans(Direction::East).map(|s| res.insert(s));
square.trans(Direction::West).map(|s| res.insert(s));
}
res
})
});
let king_moves = BySquare::new(|square| {
let mut res = Bitboard::new();
for direction in Direction::all() {
if let Some(x) = square.trans(direction) {
res |= x.bitboard();
}
}
res
});
let knight_moves = BySquare::new(|s| {
let mut res = Bitboard::new();
if let Some(s) = s.trans(Direction::North) {
s.trans(Direction::NorthEast).map(|s| res.insert(s));
s.trans(Direction::NorthWest).map(|s| res.insert(s));
}
if let Some(s) = s.trans(Direction::West) {
s.trans(Direction::NorthWest).map(|s| res.insert(s));
s.trans(Direction::SouthWest).map(|s| res.insert(s));
}
if let Some(s) = s.trans(Direction::South) {
s.trans(Direction::SouthWest).map(|s| res.insert(s));
s.trans(Direction::SouthEast).map(|s| res.insert(s));
}
if let Some(s) = s.trans(Direction::East) {
s.trans(Direction::SouthEast).map(|s| res.insert(s));
s.trans(Direction::NorthEast).map(|s| res.insert(s));
}
res
});
let magics = Magics::compute(&rays);
Self {
rays,
lines,
segments,
pawn_attacks,
king_moves,
knight_moves,
magics,
}
}
}
mod init {
use std::{mem::MaybeUninit, sync::LazyLock};
use super::Lookup;
static mut LOOKUP: MaybeUninit<Lookup> = MaybeUninit::uninit();
#[allow(static_mut_refs)]
static INIT: LazyLock<()> = LazyLock::new(|| unsafe {
LOOKUP.write(Lookup::compute());
});
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub(crate) struct InitialisedLookup(());
impl InitialisedLookup {
#[inline]
pub(crate) fn init() -> Self {
LazyLock::force(&INIT);
Self(())
}
}
impl std::ops::Deref for InitialisedLookup {
type Target = Lookup;
#[allow(static_mut_refs)]
#[inline]
fn deref(&self) -> &Self::Target {
unsafe { LOOKUP.assume_init_ref() }
}
}
}

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use crate::bitboard::*;
use crate::board::*;
use crate::rays::Rays;
const BISHOP_SHR: u8 = 55;
const ROOK_SHR: u8 = 52;
pub(crate) struct Magics {
bishop: BySquare<Magic>,
rook: BySquare<Magic>,
table: Box<[Bitboard]>,
}
#[derive(Clone, Copy)]
struct Magic {
premask: Bitboard,
factor: u64,
offset: isize,
}
impl Magics {
pub(crate) fn compute(rays: &Rays) -> Self {
let mut data = Vec::new();
let mut aux =
|shr,
factors: fn(Square) -> u64,
make_table: fn(&Rays, Square) -> (Bitboard, Vec<(Bitboard, Bitboard)>)| {
BySquare::new(|square| {
let (premask, table) = make_table(rays, square);
let factor = factors(square);
let offset = fill_table(&mut data, shr, factor, table);
Magic {
premask,
factor,
offset,
}
})
};
let bishop = aux(BISHOP_SHR, bishop_factors, make_bishop_table);
let rook = aux(ROOK_SHR, rook_factors, make_rook_table);
let mut table = Box::new_uninit_slice(data.len());
for (i, entry) in data.into_iter().enumerate() {
table[i].write(entry);
}
Self {
bishop,
rook,
table: unsafe { table.assume_init() },
}
}
#[inline]
pub(crate) fn bishop(&self, square: Square, blockers: Bitboard) -> Bitboard {
unsafe { self.get_unchecked(BISHOP_SHR, *self.bishop.get(square), blockers) }
}
#[inline]
pub(crate) fn rook(&self, square: Square, blockers: Bitboard) -> Bitboard {
unsafe { self.get_unchecked(ROOK_SHR, *self.rook.get(square), blockers) }
}
#[inline]
unsafe fn get_unchecked(&self, shr: u8, magic: Magic, blockers: Bitboard) -> Bitboard {
let Magic {
premask,
factor,
offset,
} = magic;
*self.table.get_unchecked(
((hash(shr, factor, blockers | premask) as isize).unchecked_add(offset)) as usize,
)
}
}
fn fill_table(
data: &mut Vec<Bitboard>,
shr: u8,
factor: u64,
table: Vec<(Bitboard, Bitboard)>,
) -> isize {
let offset = data.len() as isize
- table
.iter()
.map(|(x, _)| hash(shr, factor, *x) as isize)
.min()
.unwrap();
for (x, y) in &table {
let i = (hash(shr, factor, *x) as isize + offset) as usize;
while data.len() <= i {
data.push(Bitboard::new());
}
if data[i] != Bitboard::new() && data[i] != *y {
panic!();
}
data[i] = *y;
}
offset
}
fn make_bishop_table(rays: &Rays, square: Square) -> (Bitboard, Vec<(Bitboard, Bitboard)>) {
let mut premask = Bitboard::new();
for direction in [
Direction::NorthWest,
Direction::SouthWest,
Direction::SouthEast,
Direction::NorthEast,
] {
premask |= rays.ray(square, direction);
}
premask &= !Rank::First.bitboard();
premask &= !Rank::Eighth.bitboard();
premask &= !File::A.bitboard();
premask &= !File::H.bitboard();
let mut table = make_table(premask, |blockers| {
let mut res = Bitboard::new();
for direction in [
Direction::NorthWest,
Direction::SouthWest,
Direction::SouthEast,
Direction::NorthEast,
] {
res |= rays.blocked(square, direction, blockers);
}
res
});
premask = !premask;
for (x, _) in &mut table {
*x |= premask;
}
(premask, table)
}
fn make_rook_table(rays: &Rays, square: Square) -> (Bitboard, Vec<(Bitboard, Bitboard)>) {
let mut premask = Bitboard::new();
premask |= rays.ray(square, Direction::North) & !Rank::Eighth.bitboard();
premask |= rays.ray(square, Direction::West) & !File::A.bitboard();
premask |= rays.ray(square, Direction::South) & !Rank::First.bitboard();
premask |= rays.ray(square, Direction::East) & !File::H.bitboard();
let mut table = make_table(premask, |blockers| {
let mut res = Bitboard::new();
for direction in [
Direction::North,
Direction::West,
Direction::South,
Direction::East,
] {
res |= rays.blocked(square, direction, blockers);
}
res
});
premask = !premask;
for (x, _) in &mut table {
*x |= premask;
}
(premask, table)
}
fn make_table<T, F>(premask: Bitboard, f: F) -> Vec<(Bitboard, T)>
where
F: Fn(Bitboard) -> T,
{
let mut res = Vec::new();
let mut subset: u64 = 0;
loop {
subset = subset.wrapping_sub(premask.0) & premask.0;
let x = Bitboard(subset);
let y = f(x);
res.push((x, y));
if subset == 0 {
break;
}
}
res
}
fn hash(shr: u8, factor: u64, x: Bitboard) -> usize {
(x.0.wrapping_mul(factor) >> shr) as usize
}
fn bishop_factors(square: Square) -> u64 {
match square {
Square::A1 => 0x0000404040404040,
Square::B1 => 0x0040C100081000E8,
Square::C1 => 0x0000401020200000,
Square::D1 => 0x0040802004000000,
Square::E1 => 0x10403C0180000000,
Square::F1 => 0x0040210100800000,
Square::G1 => 0x0068104002008000,
Square::H1 => 0x0048082080040080,
Square::A2 => 0x0000004040404040,
Square::B2 => 0x0000002020202020,
Square::C2 => 0x00040080184001E4,
Square::D2 => 0x0040008020040000,
Square::E2 => 0x1040003C01800000,
Square::F2 => 0x0078002001008000,
Square::G2 => 0x0068001040020080,
Square::H2 => 0x0068000820010040,
Square::A3 => 0x0000400080808080,
Square::B3 => 0x0000200040404040,
Square::C3 => 0x0000400080808080,
Square::D3 => 0x0000200200801000,
Square::E3 => 0x0060200100080000,
Square::F3 => 0x0000100021C60021,
Square::G3 => 0x0000040010410040,
Square::H3 => 0x0000020008208020,
Square::A4 => 0x0000804000810100,
Square::B4 => 0x0000402000408080,
Square::C4 => 0x0000040800802080,
Square::D4 => 0x000020100C010020,
Square::E4 => 0x0000840000802000,
Square::F4 => 0x0001801800240010,
Square::G4 => 0x0000080800104100,
Square::H4 => 0x0000040400082080,
Square::A5 => 0x0000010278010040,
Square::B5 => 0x000000813C004040,
Square::C5 => 0x000001027A010040,
Square::D5 => 0x0000018180280200,
Square::E5 => 0x0000204018003080,
Square::F5 => 0x0000202040008040,
Square::G5 => 0x0000101010002080,
Square::H5 => 0x0000080808001040,
Square::A6 => 0x0000004100F90080,
Square::B6 => 0x0000002080BC0040,
Square::C6 => 0x0000004103440080,
Square::D6 => 0x0000000080FD0080,
Square::E6 => 0x0000020040100100,
Square::F6 => 0x0000404040400080,
Square::G6 => 0x000000206027D010,
Square::H6 => 0x00000008400DE806,
Square::A7 => 0x0000002101007200,
Square::B7 => 0x0000001041003900,
Square::C7 => 0x080000000F8080A0,
Square::D7 => 0x0000000008003FC0,
Square::E7 => 0x0000000100202000,
Square::F7 => 0x0000004040802000,
Square::G7 => 0x00000060401043D0,
Square::H7 => 0x00000020200413F0,
Square::A8 => 0x1400000F00410088,
Square::B8 => 0x0000000010410039,
Square::C8 => 0x000080000800807E,
Square::D8 => 0x000C69003008003F,
Square::E8 => 0x0000000001002020,
Square::F8 => 0x0000000040408020,
Square::G8 => 0x001980004010801F,
Square::H8 => 0x0000404040404040,
}
}
fn rook_factors(square: Square) -> u64 {
match square {
Square::A1 => 0x002000A28110000C,
Square::B1 => 0x0018000C01060001,
Square::C1 => 0x0040080010004004,
Square::D1 => 0x0028004084200028,
Square::E1 => 0x0030018000900300,
Square::F1 => 0x0020008020010202,
Square::G1 => 0x001800410080001F,
Square::H1 => 0x0068006801040004,
Square::A2 => 0x000028010114000A,
Square::B2 => 0x00000C0083000600,
Square::C2 => 0x0000080401020008,
Square::D2 => 0x0000200200040020,
Square::E2 => 0x0000200100020020,
Square::F2 => 0x00001800C0006018,
Square::G2 => 0x0000180070400018,
Square::H2 => 0x0000180030640018,
Square::A3 => 0x00300018010C0004,
Square::B3 => 0x0004001000080010,
Square::C3 => 0x0001000804020008,
Square::D3 => 0x0002002004002002,
Square::E3 => 0x0001002002002001,
Square::F3 => 0x0001001000801040,
Square::G3 => 0x0000004040008001,
Square::H3 => 0x0000802000200040,
Square::A4 => 0x0040200010080008,
Square::B4 => 0x0000080010040010,
Square::C4 => 0x0001020008040008,
Square::D4 => 0x0000020020040020,
Square::E4 => 0x0000010020020020,
Square::F4 => 0x0000008020010020,
Square::G4 => 0x0000008020200040,
Square::H4 => 0x0000200020004081,
Square::A5 => 0x0000081C00380020,
Square::B5 => 0x0000080400100010,
Square::C5 => 0x0000400880410010,
Square::D5 => 0x0000200200200400,
Square::E5 => 0x0000200100200200,
Square::F5 => 0x0000200080200100,
Square::G5 => 0x0000008000404001,
Square::H5 => 0x0000802000200040,
Square::A6 => 0x0000010B14002800,
Square::B6 => 0x0000030086000C00,
Square::C6 => 0x0000084040804200,
Square::D6 => 0x0000020004002020,
Square::E6 => 0x0000009001803003,
Square::F6 => 0x0000004001004002,
Square::G6 => 0x000000100800A804,
Square::H6 => 0x000000082800D002,
Square::A7 => 0x00000109040200A8,
Square::B7 => 0x000000808A050014,
Square::C7 => 0x0000004048038018,
Square::D7 => 0x0000020020040020,
Square::E7 => 0x0000002030018030,
Square::F7 => 0x0000001800E08018,
Square::G7 => 0x0000000810580050,
Square::H7 => 0x0000000C04600050,
Square::A8 => 0x0000001020891046,
Square::B8 => 0x00000080090015C1,
Square::C8 => 0x0000004005489101,
Square::D8 => 0x0000040810204002,
Square::E8 => 0x000C040810002022,
Square::F8 => 0x0008000404883002,
Square::G8 => 0x0008000400548802,
Square::H8 => 0x0000000224104486,
}
}

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use crate::bitboard::*;
use crate::board::*;
pub(crate) struct Rays(BySquare<ByDirection<Bitboard>>);
impl Rays {
pub(crate) fn new() -> Self {
Self(BySquare::new(|square| {
ByDirection::new(|direction| {
let mut square = square;
let mut res = Bitboard::new();
while let Some(x) = square.trans(direction) {
square = x;
res |= square.bitboard();
}
res
})
}))
}
#[inline]
pub(crate) fn ray(&self, square: Square, direction: Direction) -> Bitboard {
*self.0.get(square).get(direction)
}
pub(crate) fn blocked(
&self,
square: Square,
direction: Direction,
blockers: Bitboard,
) -> Bitboard {
let blockers = blockers & *self.0.get(square).get(direction);
let square2 = if (direction as u8) < 4 {
blockers.first()
} else {
blockers.last()
};
*self.0.get(square).get(direction)
& !match square2 {
Some(square2) => *self.0.get(square2).get(direction),
None => Bitboard::new(),
}
}
}

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//! Standard algebraic notation.
//!
//! SAN notation is the FIDE standard for writing moves.
//!
//! In its simplest form, it consists of the type of the moving piece followed by the target
//! square. This may be ambiguous, in which cases the origin file and/or rank is also specified.
//! The notation is shortened for pawns, and extra information may be added, to specify a capture
//! or a check.
//!
//! Examples: *`e4`*, *`Qxd8#`*, *`O-O`*, *`h7h8=Q`*
use crate::board::*;
use crate::position::*;
/// **The standard algebraic notation of a move.**
///
///
/// When converting [`San`] notation to a playable [`Move`], the optional capture flag (*x*) and
/// suffix (*+* or *#*) are ignored (as they are redundant). Thus, conversion will not fail if they
/// are incorrectly set. Similarly, conversion will not fail when the move is unnecessarily
/// disambiguated. For example, *Ke1xd1* and *Kd1* will always be equivalent, even if there is no
/// piece on *d1*.
///
/// SAN notation can be obtained from a legal move using the [`Move::to_san`] method.
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct San {
pub(crate) inner: SanInner,
pub(crate) suffix: Option<SanSuffix>,
}
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub(crate) enum SanInner {
Castle(CastlingSide),
Normal {
role: Role,
file: Option<File>,
rank: Option<Rank>,
capture: bool,
target: Square,
promotion: Option<Role>,
},
}
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub(crate) enum SanSuffix {
Check,
Checkmate,
}
impl std::fmt::Display for San {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match self.inner {
SanInner::Castle(CastlingSide::Short) => write!(f, "O-O")?,
SanInner::Castle(CastlingSide::Long) => write!(f, "O-O-O")?,
SanInner::Normal {
role,
file,
rank,
capture,
target,
promotion,
} => {
if role != Role::Pawn {
write!(f, "{}", role.to_char_uppercase())?;
}
if let Some(file) = file {
write!(f, "{}", file.to_char())?;
}
if let Some(rank) = rank {
write!(f, "{}", rank.to_char())?;
}
if capture {
write!(f, "x")?;
}
write!(f, "{}", target)?;
if let Some(promotion) = promotion {
write!(f, "={}", promotion.to_char_uppercase())?;
}
}
}
match self.suffix {
Some(SanSuffix::Check) => write!(f, "+")?,
Some(SanSuffix::Checkmate) => write!(f, "#")?,
None => (),
}
Ok(())
}
}
impl std::fmt::Debug for San {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
f.debug_tuple("San").field(&self.to_string()).finish()
}
}
impl std::str::FromStr for San {
type Err = ParseSanError;
#[inline]
fn from_str(s: &str) -> Result<Self, Self::Err> {
San::from_ascii(s.as_bytes()).ok_or(ParseSanError)
}
}
/// A syntax error when parsing [`San`] notation.
#[derive(Debug)]
pub struct ParseSanError;
impl std::fmt::Display for ParseSanError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str("invalid SAN syntax")
}
}
impl std::error::Error for ParseSanError {}
/// An error while converting [`San`] notation to a playable [`Move`].
#[derive(Debug, PartialEq, Eq)]
pub enum InvalidSan {
/// There is no move on the position that matches the SAN notation.
Illegal,
/// There is more than one move on the position that matches the SAN notation.
Ambiguous,
}
impl std::fmt::Display for InvalidSan {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let details = match self {
Self::Illegal => "illegal move",
Self::Ambiguous => "ambiguous move",
};
write!(f, "invalid SAN ({details})")
}
}
impl std::error::Error for InvalidSan {}
impl San {
/// Tries to convert SAN notation to a playable move.
///
/// This function ignores the suffix and the capture flag. It also accepts unnecessarily
/// desambiguated moves.
#[inline]
pub fn to_move<'l>(&self, position: &'l Position) -> Result<Move<'l>, InvalidSan> {
position.move_from_san(self)
}
/// Tries to read SAN notation from ascii text.
pub fn from_ascii(s: &[u8]) -> Option<Self> {
let mut r = s.iter().copied().rev();
let mut cur = r.next()?;
let suffix = match cur {
b'+' => {
cur = r.next()?;
Some(SanSuffix::Check)
}
b'#' => {
cur = r.next()?;
Some(SanSuffix::Checkmate)
}
_ => None,
};
let inner = match cur {
b'O' => SanInner::Castle({
let b'-' = r.next()? else { return None };
let b'O' = r.next()? else { return None };
match r.next() {
None => CastlingSide::Short,
Some(b'-') => {
let b'O' = r.next()? else { return None };
r.next().is_none().then_some(())?;
CastlingSide::Long
}
Some(_) => return None,
}
}),
_ => {
let promotion = Role::from_ascii(cur);
if promotion.is_some() {
(r.next()? == b'=').then_some(())?;
cur = r.next()?;
}
let target_rank = Rank::from_ascii(cur)?;
let target_file = File::from_ascii(r.next()?)?;
let target = Square::new(target_file, target_rank);
let mut cur = r.next();
let capture = cur == Some(b'x');
if capture {
cur = r.next();
}
let rank = cur.and_then(Rank::from_ascii);
if rank.is_some() {
cur = r.next();
}
let file = cur.and_then(File::from_ascii);
if file.is_some() {
cur = r.next();
}
let role = match cur {
Some(a) => {
cur = r.next();
Role::from_ascii(a)?
}
None => Role::Pawn,
};
cur.is_none().then_some(())?;
(role != Role::Pawn || file.is_some() || !capture).then_some(())?;
(role == Role::Pawn || promotion.is_none()).then_some(())?;
SanInner::Normal {
role,
file,
rank,
capture,
target,
promotion,
}
}
};
Some(Self { inner, suffix })
}
}

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//! Building chess positions.
//!
//! [`Setup`] is a builder for the [`Position`] type.
use crate::bitboard::*;
use crate::board::*;
use crate::lookup::*;
use crate::position::*;
/// **A builder type for chess positions.**
///
/// This type is useful to edit a position without having to ensure it stays legal at every step.
/// It must be validated and converted to a [`Position`] using the [`Setup::validate`] method
/// before generating moves.
///
/// This type implements [`FromStr`](std::str::FromStr) and [`Display`](std::fmt::Display) to parse
/// and print positions from text records.
///
/// Forsyth-Edwards Notation (FEN) is typically used to describe chess positions as text. eschac
/// uses a slightly different notation, which simply removes the last two fields of the FEN string
/// (i.e. the halfmove clock and the fullmove number) as the [`Position`] type does not keep
/// track of those.
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct Setup {
pub(crate) w: Bitboard,
pub(crate) p_b_q: Bitboard,
pub(crate) n_b_k: Bitboard,
pub(crate) r_q_k: Bitboard,
pub(crate) turn: Color,
pub(crate) en_passant: OptionSquare,
pub(crate) castling_rights: CastlingRights,
}
impl Setup {
/// Creates an empty board, i.e. `8/8/8/8/8/8/8/8 w - -`.
#[inline]
pub fn new() -> Self {
Self {
w: Bitboard(0),
p_b_q: Bitboard(0),
n_b_k: Bitboard(0),
r_q_k: Bitboard(0),
turn: Color::White,
en_passant: OptionSquare::None,
castling_rights: CastlingRights::new(),
}
}
/// Reads a position from an ascii record.
pub fn from_ascii(s: &[u8]) -> Result<Self, ParseSetupError> {
let mut s = s.iter().copied().peekable();
let mut setup = Setup::new();
(|| {
let mut accept_empty_square = true;
let mut rank: u8 = 7;
let mut file: u8 = 0;
for c in s.by_ref() {
if c == b'/' {
(file == 8).then_some(())?;
rank = rank.checked_sub(1)?;
file = 0;
accept_empty_square = true;
} else if (b'1'..=b'8').contains(&c) && accept_empty_square {
file = file + c - b'0';
(file <= 8).then_some(())?;
accept_empty_square = false;
} else if c == b' ' {
break;
} else {
let role = Role::from_ascii(c)?;
let color = match c.is_ascii_uppercase() {
true => Color::White,
false => Color::Black,
};
(file < 8).then_some(())?;
setup.set(
unsafe { Square::new(File::transmute(file), Rank::transmute(rank)) },
Some(Piece { role, color }),
);
file += 1;
accept_empty_square = true;
}
}
(rank == 0).then_some(())?;
(file == 8).then_some(())?;
Some(())
})()
.ok_or(ParseSetupError::InvalidBoard)?;
(|| {
match s.next()? {
b'w' => setup.set_turn(Color::White),
b'b' => setup.set_turn(Color::Black),
_ => return None,
}
(s.next()? == b' ').then_some(())
})()
.ok_or(ParseSetupError::InvalidTurn)?;
(|| {
if s.next_if_eq(&b'-').is_none() {
if s.next_if_eq(&b'K').is_some() {
setup.set_castling_rights(Color::White, CastlingSide::Short, true);
}
if s.next_if_eq(&b'Q').is_some() {
setup.set_castling_rights(Color::White, CastlingSide::Long, true);
}
if s.next_if_eq(&b'k').is_some() {
setup.set_castling_rights(Color::Black, CastlingSide::Short, true);
}
if s.next_if_eq(&b'q').is_some() {
setup.set_castling_rights(Color::Black, CastlingSide::Long, true);
}
}
(s.next()? == b' ').then_some(())
})()
.ok_or(ParseSetupError::InvalidCastlingRights)?;
(|| {
match s.next()? {
b'-' => (),
file => setup.set_en_passant_target_square(Some(Square::new(
File::from_ascii(file)?,
Rank::from_ascii(s.next()?)?,
))),
}
s.next().is_none().then_some(())
})()
.ok_or(ParseSetupError::InvalidEnPassantTargetSquare)?;
Ok(setup)
}
/// Returns the occupancy of a square.
#[inline]
pub fn get(&self, square: Square) -> Option<Piece> {
Some(Piece {
role: self.get_role(square)?,
color: match (self.w & square.bitboard()).is_empty() {
false => Color::White,
true => Color::Black,
},
})
}
/// Returns the color to play.
#[inline]
pub fn turn(&self) -> Color {
self.turn
}
/// Returns `true` if castling is available for the given color and side.
#[inline]
pub fn castling_rights(&self, color: Color, side: CastlingSide) -> bool {
self.castling_rights.get(color, side)
}
/// Returns the optional en passant target square.
#[inline]
pub fn en_passant_target_square(&self) -> Option<Square> {
self.en_passant.try_into_square()
}
/// Sets the occupancy of a square.
#[inline]
pub fn set(&mut self, square: Square, piece: Option<Piece>) {
let mask = !square.bitboard();
self.w &= mask;
self.p_b_q &= mask;
self.n_b_k &= mask;
self.r_q_k &= mask;
if let Some(piece) = piece {
let to = square.bitboard();
match piece.color {
Color::White => self.w |= to,
Color::Black => (),
}
match piece.role {
Role::Pawn => {
self.p_b_q |= to;
}
Role::Knight => {
self.n_b_k |= to;
}
Role::Bishop => {
self.p_b_q |= to;
self.n_b_k |= to;
}
Role::Rook => {
self.r_q_k |= to;
}
Role::Queen => {
self.p_b_q |= to;
self.r_q_k |= to;
}
Role::King => {
self.n_b_k |= to;
self.r_q_k |= to;
}
}
}
}
/// Sets the color to play.
#[inline]
pub fn set_turn(&mut self, color: Color) {
self.turn = color;
}
/// Sets the castling rights for the given color and side.
#[inline]
pub fn set_castling_rights(&mut self, color: Color, side: CastlingSide, value: bool) {
match value {
true => self.castling_rights.set(color, side),
false => self.castling_rights.unset(color, side),
}
}
/// Sets the en passant target square.
#[inline]
pub fn set_en_passant_target_square(&mut self, square: Option<Square>) {
self.en_passant = OptionSquare::new(square);
}
/// Returns the mirror image of the position.
///
/// The mirror of a position is the position obtained after reflecting the placement of pieces
/// horizontally, inverting the color of all the pieces, inverting the turn, and reflecting the
/// castling rights as well as the en passant target square.
///
/// For example, the mirror image of `rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b Kq e3`
/// is `rnbqkbnr/pppp1ppp/8/4p3/8/8/PPPPPPPP/RNBQKBNR w Qk e6`.
#[inline]
pub fn mirror(&self) -> Self {
Self {
w: (self.w ^ (self.p_b_q | self.n_b_k | self.r_q_k)).mirror(),
p_b_q: self.p_b_q.mirror(),
n_b_k: self.n_b_k.mirror(),
r_q_k: self.r_q_k.mirror(),
turn: !self.turn,
en_passant: self
.en_passant
.try_into_square()
.map(|square| OptionSquare::from_square(square.mirror()))
.unwrap_or(OptionSquare::None),
castling_rights: self.castling_rights.mirror(),
}
}
/// Tries to validate the position, i.e. converting it to a [`Position`].
///
/// See [`IllegalPositionReason`] for details.
pub fn validate(self) -> Result<Position, IllegalPosition> {
debug_assert!((self.w & !(self.p_b_q | self.n_b_k | self.r_q_k)).is_empty());
debug_assert!((self.p_b_q & self.n_b_k & self.r_q_k).is_empty());
let mut reasons = IllegalPositionReasons::new();
let d = InitialisedLookup::init();
let blockers = self.p_b_q | self.n_b_k | self.r_q_k;
let pieces = self.bitboards();
if Color::all()
.into_iter()
.any(|color| pieces.get(color).king().is_empty())
{
reasons.add(IllegalPositionReason::MissingKing);
}
if Color::all()
.into_iter()
.any(|color| pieces.get(color).get(Role::King).len() > 1)
{
reasons.add(IllegalPositionReason::TooManyKings);
}
if pieces.get(!self.turn).king().any(|enemy_king| {
let pieces = pieces.get(self.turn);
!(d.king(enemy_king) & *pieces.get(Role::King)
| d.bishop(enemy_king, blockers)
& (*pieces.get(Role::Queen) | *pieces.get(Role::Bishop))
| d.rook(enemy_king, blockers)
& (*pieces.get(Role::Queen) | *pieces.get(Role::Rook))
| d.knight(enemy_king) & *pieces.get(Role::Knight)
| d.pawn_attack(!self.turn, enemy_king) & *pieces.get(Role::Pawn))
.is_empty()
}) {
reasons.add(IllegalPositionReason::HangingKing);
}
if Color::all().into_iter().any(|color| {
!(*pieces.get(color).get(Role::Pawn)
& (Rank::First.bitboard() | Rank::Eighth.bitboard()))
.is_empty()
}) {
reasons.add(IllegalPositionReason::PawnOnBackRank);
}
if Color::all().into_iter().any(|color| {
let dark_squares = Bitboard(0xAA55AA55AA55AA55);
let light_squares = Bitboard(0x55AA55AA55AA55AA);
let pieces = pieces.get(color);
pieces.get(Role::Pawn).len()
+ pieces.get(Role::Queen).len().saturating_sub(1)
+ (*pieces.get(Role::Bishop) & dark_squares)
.len()
.saturating_sub(1)
+ (*pieces.get(Role::Bishop) & light_squares)
.len()
.saturating_sub(1)
+ pieces.get(Role::Knight).len().saturating_sub(2)
+ pieces.get(Role::Rook).len().saturating_sub(2)
> 8
}) {
reasons.add(IllegalPositionReason::TooMuchMaterial);
}
if Color::all().into_iter().any(|color| {
CastlingSide::all().into_iter().any(|side| {
self.castling_rights.get(color, side)
&& !(pieces
.get(color)
.get(Role::King)
.contains(Square::new(File::E, color.home_rank()))
&& pieces
.get(color)
.get(Role::Rook)
.contains(Square::new(side.rook_origin_file(), color.home_rank())))
})
}) {
reasons.add(IllegalPositionReason::InvalidCastlingRights);
}
if self.en_passant.try_into_square().is_some_and(|en_passant| {
let (target_rank, pawn_rank) = match self.turn {
Color::White => (Rank::Sixth, Rank::Fifth),
Color::Black => (Rank::Third, Rank::Fourth),
};
let pawn_square = Square::new(en_passant.file(), pawn_rank);
en_passant.rank() != target_rank
|| blockers.contains(en_passant)
|| !pieces.get(!self.turn).get(Role::Pawn).contains(pawn_square)
}) {
reasons.add(IllegalPositionReason::InvalidEnPassant);
}
if self.en_passant.try_into_square().is_some_and(|en_passant| {
let blockers = blockers
& !en_passant.bitboard().trans(match self.turn {
Color::White => Direction::South,
Color::Black => Direction::North,
});
pieces
.get(self.turn)
.king()
.first()
.is_some_and(|king_square| {
!(d.bishop(king_square, blockers)
& (pieces.get(!self.turn).queen() | pieces.get(!self.turn).bishop()))
.is_empty()
})
}) {
reasons.add(IllegalPositionReason::ImpossibleEnPassantPin);
}
if reasons.0 != 0 {
Err(IllegalPosition {
setup: self,
reasons,
})
} else {
Ok(unsafe { Position::from_setup(self) })
}
}
#[inline]
pub(crate) fn get_role(&self, square: Square) -> Option<Role> {
let mask = square.bitboard();
let bit0 = (self.p_b_q & mask).0 >> square as u8;
let bit1 = (self.n_b_k & mask).0 >> square as u8;
let bit2 = (self.r_q_k & mask).0 >> square as u8;
match bit0 | bit1 << 1 | bit2 << 2 {
0 => None,
i => Some(unsafe { Role::transmute(i as u8) }),
}
}
#[inline]
pub(crate) fn bitboards(&self) -> ByColor<ByRole<Bitboard>> {
let Self {
w,
p_b_q,
n_b_k,
r_q_k,
..
} = self.clone();
let k = n_b_k & r_q_k;
let q = p_b_q & r_q_k;
let b = p_b_q & n_b_k;
let n = n_b_k ^ b ^ k;
let r = r_q_k ^ q ^ k;
let p = p_b_q ^ b ^ q;
ByColor::new(|color| {
let mask = match color {
Color::White => w,
Color::Black => !w,
};
ByRole::new(|kind| {
mask & match kind {
Role::King => k,
Role::Queen => q,
Role::Bishop => b,
Role::Knight => n,
Role::Rook => r,
Role::Pawn => p,
}
})
})
}
}
impl std::fmt::Debug for Setup {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
f.debug_tuple("Setup").field(&self.to_string()).finish()
}
}
impl std::fmt::Display for Setup {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
use std::fmt::Write;
for rank in Rank::all().into_iter().rev() {
let mut count = 0;
for file in File::all() {
match self.get(Square::new(file, rank)) {
Some(piece) => {
if count > 0 {
f.write_char(char::from_u32('0' as u32 + count).unwrap())?;
}
count = 0;
f.write_char(match piece.color {
Color::White => piece.role.to_char_uppercase(),
Color::Black => piece.role.to_char_lowercase(),
})?;
}
None => {
count += 1;
}
}
}
if count > 0 {
f.write_char(char::from_u32('0' as u32 + count).unwrap())?;
}
if rank != Rank::First {
f.write_char('/')?;
}
}
f.write_char(' ')?;
f.write_char(match self.turn {
Color::White => 'w',
Color::Black => 'b',
})?;
f.write_char(' ')?;
let mut no_castle_available = true;
if self.castling_rights(Color::White, CastlingSide::Short) {
f.write_char('K')?;
no_castle_available = false;
}
if self.castling_rights(Color::White, CastlingSide::Long) {
f.write_char('Q')?;
no_castle_available = false;
}
if self.castling_rights(Color::Black, CastlingSide::Short) {
f.write_char('k')?;
no_castle_available = false;
}
if self.castling_rights(Color::Black, CastlingSide::Long) {
f.write_char('q')?;
no_castle_available = false;
}
if no_castle_available {
f.write_char('-')?;
}
f.write_char(' ')?;
match self.en_passant.try_into_square() {
Some(sq) => {
f.write_str(sq.to_str())?;
}
None => {
write!(f, "-")?;
}
}
Ok(())
}
}
impl std::str::FromStr for Setup {
type Err = ParseSetupError;
#[inline]
fn from_str(s: &str) -> Result<Self, Self::Err> {
Self::from_ascii(s.as_bytes())
}
}
/// An error when trying to parse a position record.
///
/// The variant indicates the field that caused the error.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ParseSetupError {
InvalidBoard,
InvalidTurn,
InvalidCastlingRights,
InvalidEnPassantTargetSquare,
}
impl std::fmt::Display for ParseSetupError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let details = match self {
Self::InvalidBoard => "board",
Self::InvalidTurn => "turn",
Self::InvalidCastlingRights => "castling rights",
Self::InvalidEnPassantTargetSquare => "en passant target square",
};
write!(f, "invalid text record ({details})")
}
}
impl std::error::Error for ParseSetupError {}
/// An invalid position.
///
/// This is an illegal position that can't be represented with the [`Position`] type.
#[derive(Debug)]
pub struct IllegalPosition {
setup: Setup,
reasons: IllegalPositionReasons,
}
impl std::fmt::Display for IllegalPosition {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
use std::fmt::Write;
let setup = &self.setup;
write!(f, "`{setup}` is illegal:")?;
let mut first = true;
for reason in self.reasons {
if !first {
f.write_char(',')?;
}
first = false;
write!(f, " {reason}")?;
}
Ok(())
}
}
impl std::error::Error for IllegalPosition {}
impl IllegalPosition {
/// Returns an iterator over the reasons why the position is rejected.
pub fn reasons(&self) -> IllegalPositionReasons {
self.reasons
}
/// Returns the [`Setup`] that failed validation.
pub fn as_setup(&self) -> &Setup {
&self.setup
}
/// Returns the [`Setup`] that failed validation.
pub fn into_setup(self) -> Setup {
self.setup
}
}
/// A set of [`IllegalPositionReason`]s.
#[derive(Clone, Copy)]
pub struct IllegalPositionReasons(u8);
impl std::fmt::Debug for IllegalPositionReasons {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_list().entries(*self).finish()
}
}
impl IllegalPositionReasons {
/// Returns `true` if the given reason appears in the set.
pub fn contains(&self, reason: IllegalPositionReason) -> bool {
(self.0 & reason as u8) != 0
}
fn new() -> Self {
IllegalPositionReasons(0)
}
fn add(&mut self, reason: IllegalPositionReason) {
self.0 |= reason as u8;
}
}
impl Iterator for IllegalPositionReasons {
type Item = IllegalPositionReason;
fn next(&mut self) -> Option<Self::Item> {
if self.0 == 0 {
None
} else {
let reason = 1 << self.0.trailing_zeros();
self.0 &= !reason;
Some(unsafe { std::mem::transmute::<u8, IllegalPositionReason>(reason) })
}
}
}
/// Reasons for illegal positions to be rejected by eschac.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub enum IllegalPositionReason {
/// One of the colors misses its king.
MissingKing = 1,
/// There is more than one king of the same color.
TooManyKings = 2,
/// The opponent's king is in check.
HangingKing = 4,
/// There is a pawn on the first or eighth rank.
PawnOnBackRank = 8,
/// Some castling rights are invalid regarding the positions of the rooks and kings.
InvalidCastlingRights = 16,
/// The en passant target square is invalid, either because:
/// - it is not on the correct rank
/// - it is occupied
/// - it is not behind an opponent's pawn
InvalidEnPassant = 32,
/// There is an impossible number of pieces.
///
/// Enforcing this enables to put an upper limit on the number of legal moves on any position,
/// allowing to reduce the size of [`Moves`].
TooMuchMaterial = 64,
/// The pawn that can be taken en passant is pinned diagonally to the playing king.
///
/// This can't happen on a legal position, as it would imply that the king could have be taken
/// on that move. Enforcing this makes it unnecessary to test for a discovery check on the
/// diagonal when taking en passant.
ImpossibleEnPassantPin = 128,
}
impl std::fmt::Display for IllegalPositionReason {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str(match self {
Self::MissingKing => "missing king",
Self::TooManyKings => "too many kings",
Self::HangingKing => "hanging king",
Self::PawnOnBackRank => "pawn on back rank",
Self::InvalidCastlingRights => "invalid castling rights",
Self::InvalidEnPassant => "invalid en passant",
Self::TooMuchMaterial => "too much material",
Self::ImpossibleEnPassantPin => "illegal en passant",
})
}
}

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//! UCI notation.
//!
//! Move notation as defined by the Universal Chess Interface standard used for most chess engines
//! and chess servers.
//!
//! A move is described by its origin and target squares. Castling is described as the move done by
//! the king. For promotion, a lowercase letter is added at the end of the move.
//!
//! Examples: *`e2e4`*, *`d1d8`*, *`e1g1`* (short castling), *`h7h8q`* (promotion)
use crate::board::*;
use crate::position::*;
/// **The UCI notation of a move.**
///
/// UCI notation can be obtained from a legal move using the [`Move::to_uci`] method.
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct UciMove {
pub from: Square,
pub to: Square,
pub promotion: Option<Role>,
}
impl std::fmt::Display for UciMove {
#[inline]
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
write!(f, "{}{}", self.from, self.to)?;
if let Some(promotion) = self.promotion {
write!(f, "{}", promotion.to_char_lowercase())?;
}
Ok(())
}
}
impl std::fmt::Debug for UciMove {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
f.debug_tuple("UciMove").field(&self.to_string()).finish()
}
}
impl std::str::FromStr for UciMove {
type Err = ParseUciMoveError;
#[inline]
fn from_str(s: &str) -> Result<Self, Self::Err> {
Self::from_ascii(s.as_bytes()).ok_or(ParseUciMoveError)
}
}
/// A syntax error when parsing a [`UciMove`].
#[derive(Debug)]
pub struct ParseUciMoveError;
impl std::fmt::Display for ParseUciMoveError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str("invalid UCI notation")
}
}
impl std::error::Error for ParseUciMoveError {}
/// An error when converting [`UciMove`] notation to a playable [`Move`].
#[derive(Debug)]
pub enum InvalidUciMove {
/// The is no move on the position that matches the UCI notation.
Illegal,
}
impl std::fmt::Display for InvalidUciMove {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str("illegal UCI move")
}
}
impl std::error::Error for InvalidUciMove {}
impl UciMove {
/// Tries to convert UCI notation to a playable move.
#[inline]
pub fn to_move<'l>(&self, position: &'l Position) -> Result<Move<'l>, InvalidUciMove> {
position.move_from_uci(*self)
}
/// Tries to read UCI notation from ascii text.
#[inline]
pub fn from_ascii(s: &[u8]) -> Option<Self> {
match s {
[a, b, c, d, s @ ..] => Some(Self {
from: Square::new(File::from_ascii(*a)?, Rank::from_ascii(*b)?),
to: Square::new(File::from_ascii(*c)?, Rank::from_ascii(*d)?),
promotion: match s {
[] => None,
[c] => Some(Role::from_ascii(*c)?),
_ => return None,
},
}),
_ => None,
}
}
}

302
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use eschac::board::*;
use eschac::position::*;
use eschac::san::*;
use eschac::setup::*;
static P1: &'static str = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq -";
static P2: &'static str = "r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq -";
static P3: &'static str = "8/2p5/3p4/KP5r/1R3p1k/8/4P1P1/8 w - -";
static P4: &'static str = "r3k2r/Pppp1ppp/1b3nbN/nP6/BBP1P3/q4N2/Pp1P2PP/R2Q1RK1 w kq -";
static P5: &'static str = "rnbq1k1r/pp1Pbppp/2p5/8/2B5/8/PPP1NnPP/RNBQK2R w KQ -";
static P6: &'static str = "r4rk1/1pp1qppp/p1np1n2/2b1p1B1/2B1P1b1/P1NP1N2/1PP1QPPP/R4RK1 w - -";
fn recursive_check_aux(position: Position, depth: usize) {
assert_eq!(
position,
position
.as_setup()
.to_string()
.parse::<Setup>()
.unwrap()
.validate()
.unwrap(),
);
if let Some(passed) = position.pass() {
let mut position = position.clone();
position.remove_en_passant_target_square();
assert_eq!(position, passed.pass().unwrap());
}
let computed_mirror = {
let mut setup = Setup::new();
for square in Square::all() {
setup.set(
square.mirror(),
position.get(square).map(|piece| Piece {
role: piece.role,
color: !piece.color,
}),
);
}
setup.set_turn(!position.turn());
for color in Color::all() {
for side in CastlingSide::all() {
setup.set_castling_rights(!color, side, position.castling_rights(color, side));
}
}
setup.set_en_passant_target_square(
position
.en_passant_target_square()
.map(|square| square.mirror()),
);
setup.validate().unwrap()
};
let expected_mirror = position.mirror();
assert_eq!(computed_mirror, expected_mirror);
assert_eq!(expected_mirror.mirror(), position);
match depth.checked_sub(1) {
None => (),
Some(depth) => {
position.legal_moves().into_iter().for_each(|m| {
let uci = m.to_uci();
assert_eq!(uci, uci.to_move(&position).unwrap().to_uci());
let san: San = m.to_san();
match san.to_move(&position) {
Ok(m) => assert_eq!(san, m.to_san()),
Err(err) => {
panic!("{san} is {err} on {position:?}")
}
};
recursive_check_aux(m.make(), depth)
});
}
}
}
fn recursive_check(record: &str) {
recursive_check_aux(record.parse::<Setup>().unwrap().validate().unwrap(), 4);
}
#[test]
fn recursive_check_1() {
recursive_check(P1);
}
#[test]
fn recursive_check_2() {
recursive_check(P2);
}
#[test]
fn recursive_check_3() {
recursive_check(P3);
}
#[test]
fn recursive_check_4() {
recursive_check(P4);
}
#[test]
fn recursive_check_5() {
recursive_check(P5);
}
#[test]
fn recursive_check_6() {
recursive_check(P6);
}
#[test]
fn setup() {
assert_eq!(Position::new().as_setup().to_string(), P1);
assert_eq!(Setup::new().to_string(), "8/8/8/8/8/8/8/8 w - -");
assert_eq!(
"8/8/8/8/1Pp5/8/R1k5/K7 w - b3"
.parse::<Setup>()
.unwrap()
.to_string(),
"8/8/8/8/1Pp5/8/R1k5/K7 w - b3",
);
for (record, err) in [
("", ParseSetupError::InvalidBoard),
(" w - -", ParseSetupError::InvalidBoard),
("8/8/8/8/8/8/8 w - -", ParseSetupError::InvalidBoard),
("1/1/1/1/1/1/1/1 w - -", ParseSetupError::InvalidBoard),
(
"44/44/44/44/44/44/44/44 w - -",
ParseSetupError::InvalidBoard,
),
("8/8/8/8/8/8/8/8/8 w - -", ParseSetupError::InvalidBoard),
("p8/8/8/8/8/8/8/8 w - -", ParseSetupError::InvalidBoard),
("8/8/8/8/8/8/8/8 - - - ", ParseSetupError::InvalidTurn),
(
"8/8/8/8/8/8/8/8 w QQQQ -",
ParseSetupError::InvalidCastlingRights,
),
] {
assert_eq!(record.parse::<Setup>(), Err(err), "{record}");
}
for (record, reason) in [
(
"8/8/8/8/8/8/8/8 w KQkq -",
IllegalPositionReason::MissingKing,
),
(
"3kk3/8/8/8/8/8/8/3KK3 w KQkq -",
IllegalPositionReason::TooManyKings,
),
(
"4k3/8/8/1Q6/8/8/8/4K3 w - -",
IllegalPositionReason::HangingKing,
),
(
"4k3/8/3N4/8/8/8/8/4K3 w - -",
IllegalPositionReason::HangingKing,
),
(
"4k3/8/8/8/8/8/8/4K2R w KQ -",
IllegalPositionReason::InvalidCastlingRights,
),
(
"4k3/8/8/8/8/8/8/P3K3 w KQ -",
IllegalPositionReason::PawnOnBackRank,
),
(
"p3k3/8/8/8/8/8/8/4K3 w KQ -",
IllegalPositionReason::PawnOnBackRank,
),
(
"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR b KQkq e3",
IllegalPositionReason::InvalidEnPassant,
),
(
"rnbqkbnr/pppppppp/8/8/8/4P3/PPPP1PPP/RNBQKBNR b KQkq e3",
IllegalPositionReason::InvalidEnPassant,
),
(
"rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR w KQkq e3",
IllegalPositionReason::InvalidEnPassant,
),
(
"8/8/8/5B2/4P3/3k4/8/4K3 b - e3",
IllegalPositionReason::ImpossibleEnPassantPin,
),
(
"8/8/8/3k4/4P3/5B2/8/4K3 b - e3",
IllegalPositionReason::ImpossibleEnPassantPin,
),
(
"rnbqkbnr/pppppppp/8/8/4B3/8/PPPPPPPP/RNBQKBNR b KQkq -",
IllegalPositionReason::TooMuchMaterial,
),
(
"rnbqkbnr/pppppppp/8/8/8/QBNP4/PPPPPPP1/RNBQKBNR b KQkq -",
IllegalPositionReason::TooMuchMaterial,
),
] {
assert!(
record.parse::<Setup>().map(|record| record.to_string()) == Ok(record.to_string()),
"{record}",
);
assert!(
record
.parse::<Setup>()
.unwrap()
.validate()
.is_err_and(|e| e.reasons().contains(reason)),
"{record} should be invalid because of {reason:?}",
);
}
for record in [
"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPB/RNBQKBNR b KQkq -",
"rnbqkbnr/pppppppp/8/8/8/8/NNNNNNNN/RNBQKBNR b KQkq -",
"rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3",
"3kr3/8/8/8/4P3/8/8/4K3 b - e3",
"8/8/8/3k4/3P4/8/8/3RK3 b - d3",
] {
assert!(record.parse::<Setup>().is_ok(), "{record}");
}
}
#[test]
fn mirror() {
assert_eq!(Position::new().pass(), Some(Position::new().mirror()));
let position = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b Kq e3"
.parse::<Setup>()
.unwrap()
.validate()
.unwrap();
let mirror = "rnbqkbnr/pppp1ppp/8/4p3/8/8/PPPPPPPP/RNBQKBNR w Qk e6"
.parse::<Setup>()
.unwrap()
.validate()
.unwrap();
assert_eq!(mirror, position.mirror());
}
fn perft_aux(record: &str, tests: &[u128]) {
let position = record.parse::<Setup>().unwrap().validate().unwrap();
for (depth, value) in tests.iter().copied().enumerate() {
assert_eq!(
position.perft(depth),
value,
"\"{record}\" at depth {depth}",
);
}
}
#[test]
fn perft_1() {
perft_aux(P1, &[1, 20, 400, 8_902, 197_281, 4_865_609, 119_060_324]);
}
#[test]
fn perft_2() {
perft_aux(P2, &[1, 48, 2039, 97_862, 4_085_603, 193_690_690]);
}
#[test]
fn perft_3() {
perft_aux(
P3,
&[1, 14, 191, 2_812, 43_238, 674_624, 11_030_083, 178_633_661],
);
}
#[test]
fn perft_4() {
perft_aux(P4, &[1, 6, 264, 9_467, 422_333, 15_833_292]);
}
#[test]
fn perft_5() {
perft_aux(P5, &[1, 44, 1_486, 62_379, 2_103_487, 89_941_194]);
}
#[test]
fn perft_6() {
perft_aux(P6, &[1, 46, 2_079, 89_890, 3_894_594, 164_075_551]);
}
#[test]
fn san() {
let position = "8/2KN1p2/5p2/3N1B1k/5PNp/7P/7P/8 w - -"
.parse::<Setup>()
.unwrap()
.validate()
.unwrap();
let san1 = "N7xf6#".parse::<San>().unwrap();
let m1 = san1.to_move(&position).unwrap();
let san2 = "N5xf6#".parse::<San>().unwrap();
let m2 = san2.to_move(&position).unwrap();
let san3 = "Ngxf6+".parse::<San>().unwrap();
let m3 = san3.to_move(&position).unwrap();
assert_eq!(m1.to_san(), san1);
assert_eq!(m2.to_san(), san2);
assert_eq!(m3.to_san(), san3);
assert_eq!(
"Nd7f6"
.parse::<San>()
.unwrap()
.to_move(&position)
.unwrap()
.to_san(),
san1,
);
assert_eq!(
"Nf6".parse::<San>().unwrap().to_move(&position).map(|_| ()),
Err(InvalidSan::Ambiguous),
);
}