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[board] Add a "count leading zeros" implementation for ARM machines

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Call the `clz` instruction on the bitboard via `asm!`.
This commit is contained in:
Eryn Wells 2023-12-21 08:17:17 -08:00
parent 4eb734d3eb
commit ed9a919db6
1 changed files with 24 additions and 0 deletions
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24
board/src/bitboard.rs
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@ -1,6 +1,7 @@
// Eryn Wells <eryn@erynwells.me> // Eryn Wells <eryn@erynwells.me>
use crate::square::Square; use crate::square::Square;
use std::arch::asm;
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)] #[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct BitBoard(pub u64); pub struct BitBoard(pub u64);
@ -17,6 +18,20 @@ impl BitBoard {
fn place_piece_at(&mut self, sq: &Square) { fn place_piece_at(&mut self, sq: &Square) {
self.0 |= 1 << sq.index self.0 |= 1 << sq.index
} }
#[cfg(target_arch = "arm")]
fn _arm_count_leading_zeros(&self) -> u8 {
let mut number_of_leading_zeros: u8 = 0;
unsafe {
asm!(
"clz {count}, {bitfield}",
count = out(reg) number_of_leading_zeros,
bitfield = in(reg) self.0,
);
}
number_of_leading_zeros
}
} }
#[cfg(test)] #[cfg(test)]
@ -47,4 +62,13 @@ mod tests {
bb.place_piece_at(&Square::from_index(34).expect("Invalid square index")); bb.place_piece_at(&Square::from_index(34).expect("Invalid square index"));
assert!(bb.has_piece_at(&Square::from_index(34).expect("Invalid square index"))); assert!(bb.has_piece_at(&Square::from_index(34).expect("Invalid square index")));
} }
#[cfg(target_arch = "arm")]
#[test]
fn arm_count_leading_zeros() {
assert_eq!(BitBoard(0)._arm_count_leading_zeros(), 0);
assert_eq!(BitBoard(0b10)._arm_count_leading_zeros(), 62);
assert_eq!(BitBoard(0b1010)._arm_count_leading_zeros(), 60);
assert_eq!(BitBoard(0x80000000)._arm_count_leading_zeros(), 0);
}
} }