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Fix CastleRights unsound interface #61

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Fix CastleRights unsound interface #61

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fa93359
Remove unsafe from public method CasteRights::from_index. Add unsafe …
shumpohl Jun 24, 2021
02f52e7
Add safety comments
shumpohl Jun 24, 2021
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34 changes: 25 additions & 9 deletions src/castle_rights.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ use crate::magic::{KINGSIDE_CASTLE_SQUARES, QUEENSIDE_CASTLE_SQUARES};

/// What castle rights does a particular player have?
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Debug, Hash)]
#[repr(u8)]
pub enum CastleRights {
NoRights,
KingSide,
Expand Down Expand Up @@ -51,6 +52,12 @@ const CASTLES_PER_SQUARE: [[u8; 64]; 2] = [
];

impl CastleRights {
/// SAFETY: value must be smaller NUM_CASTLE_RIGHTS
unsafe fn new_unchecked(value: usize) -> CastleRights {
debug_assert!(value < NUM_CASTLE_RIGHTS);
std::mem::transmute(value as u8)
}

/// Can I castle kingside?
pub fn has_kingside(&self) -> bool {
self.to_index() & 1 == 1
Expand All @@ -62,11 +69,14 @@ impl CastleRights {
}

pub fn square_to_castle_rights(color: Color, sq: Square) -> CastleRights {
CastleRights::from_index(unsafe {
*CASTLES_PER_SQUARE
.get_unchecked(color.to_index())
.get_unchecked(sq.to_index())
} as usize)
unsafe {
// SAFETY: All values in constant are < 4
CastleRights::new_unchecked(
*CASTLES_PER_SQUARE
.get_unchecked(color.to_index())
.get_unchecked(sq.to_index()) as usize
)
}
}

/// What squares need to be empty to castle kingside?
Expand All @@ -81,12 +91,18 @@ impl CastleRights {

/// Remove castle rights, and return a new `CastleRights`.
pub fn remove(&self, remove: CastleRights) -> CastleRights {
CastleRights::from_index(self.to_index() & !remove.to_index())
unsafe {
// SAFETY: x < 4 => (x & y) < 4
CastleRights::new_unchecked(self.to_index() & !remove.to_index())
}
}

/// Add some castle rights, and return a new `CastleRights`.
pub fn add(&self, add: CastleRights) -> CastleRights {
CastleRights::from_index(self.to_index() | add.to_index())
unsafe {
// SAFETY: x < 4 && y < 4 => (x | y) < 4
CastleRights::new_unchecked(self.to_index() | add.to_index())
}
}

/// Convert `CastleRights` to `usize` for table lookups
Expand All @@ -101,7 +117,7 @@ impl CastleRights {
1 => CastleRights::KingSide,
2 => CastleRights::QueenSide,
3 => CastleRights::Both,
_ => unsafe { unreachable_unchecked() },
_ => unreachable!()
}
}

Expand Down Expand Up @@ -149,7 +165,7 @@ impl CastleRights {
match square.get_file() {
File::A => CastleRights::QueenSide,
File::H => CastleRights::KingSide,
_ => unsafe { unreachable_unchecked() },
_ => unreachable!(),
}
}
}