Eryn Wells
2394afc210
This bit scanner iterates populated bits in a BitBoard from the trailing (least-significant) end. Rename BitScanner → LeadingBitScanner. Factor implementation of these two into a macro. Clean up iterator returned by BitBoard::occupied_squares Implement BitBoard::occupied_squares_trailing
122 lines
3 KiB
Rust
122 lines
3 KiB
Rust
// Eryn Wells <eryn@erynwells.me>
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macro_rules! bit_scanner {
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($name:ident) => {
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pub(crate) struct $name {
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bits: u64,
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shift: usize,
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}
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impl $name {
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pub(crate) fn new(bits: u64) -> Self {
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Self { bits, shift: 0 }
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}
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}
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};
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}
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bit_scanner!(LeadingBitScanner);
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bit_scanner!(TrailingBitScanner);
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impl Iterator for LeadingBitScanner {
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type Item = usize;
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fn next(&mut self) -> Option<Self::Item> {
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let u64bits = u64::BITS as usize;
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if self.shift == u64bits {
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return None;
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}
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let shifted_bits = self.bits << self.shift;
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let leading_zeros = shifted_bits.leading_zeros() as usize;
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if leading_zeros == u64bits {
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self.shift = leading_zeros;
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return None;
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}
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let position = u64bits - (self.shift + leading_zeros + 1);
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// Shift 1 additional place to account for the 1 that `leading_zeros` found.
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self.shift += leading_zeros + 1;
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Some(position)
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}
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}
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impl Iterator for TrailingBitScanner {
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type Item = usize;
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fn next(&mut self) -> Option<Self::Item> {
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let u64bits = u64::BITS as usize;
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if self.shift == u64bits {
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return None;
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}
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let shifted_bits = self.bits >> self.shift;
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let trailing_zeros = shifted_bits.trailing_zeros() as usize;
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if trailing_zeros == u64bits {
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self.shift = trailing_zeros;
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return None;
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}
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let position = self.shift + trailing_zeros;
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// Shift 1 additional place to account for the 1 that `leading_zeros` found.
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self.shift += trailing_zeros + 1;
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Some(position)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn leading_zero() {
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let mut scanner = LeadingBitScanner::new(0);
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assert_eq!(scanner.next(), None);
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}
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#[test]
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fn leading_one() {
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let mut scanner = LeadingBitScanner::new(1);
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assert_eq!(scanner.next(), Some(0));
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assert_eq!(scanner.next(), None);
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}
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#[test]
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fn leading_complex() {
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let mut scanner = LeadingBitScanner::new(0b11000101);
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assert_eq!(scanner.next(), Some(7));
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assert_eq!(scanner.next(), Some(6));
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assert_eq!(scanner.next(), Some(2));
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assert_eq!(scanner.next(), Some(0));
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assert_eq!(scanner.next(), None);
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}
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#[test]
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fn trailing_zero() {
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let mut scanner = TrailingBitScanner::new(0);
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assert_eq!(scanner.next(), None);
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}
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#[test]
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fn trailing_one() {
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let mut scanner = TrailingBitScanner::new(1);
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assert_eq!(scanner.next(), Some(0));
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assert_eq!(scanner.next(), None);
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}
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#[test]
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fn trailing_complex() {
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let mut scanner = TrailingBitScanner::new(0b11000101);
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assert_eq!(scanner.next(), Some(0));
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assert_eq!(scanner.next(), Some(2));
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assert_eq!(scanner.next(), Some(6));
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assert_eq!(scanner.next(), Some(7));
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assert_eq!(scanner.next(), None);
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}
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}
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