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//! Defines constants and functions for working with bitboards. //! //! `u64` bit-sets called *bitboards* can be used to represent a set //! of squares on the chessboard. This module defines utility //! functions and constants for working with `u64` bit-sets. //! //! **Note:** "LSB" means "least significant `1` bit". use board::{Square, Bitboard}; /// Empty set of squares. pub const BB_NONE: Bitboard = 0; /// The set of all 64 squares on the board. pub const BB_ALL: Bitboard = 0xffffffffffffffff; /// The squares on rank 1. pub const BB_RANK_1: Bitboard = 0b11111111; /// The squares on rank 2. pub const BB_RANK_2: Bitboard = BB_RANK_1 << 8; /// The squares on rank 3. pub const BB_RANK_3: Bitboard = BB_RANK_2 << 8; /// The squares on rank 4. pub const BB_RANK_4: Bitboard = BB_RANK_3 << 8; /// The squares on rank 5. pub const BB_RANK_5: Bitboard = BB_RANK_4 << 8; /// The squares on rank 6. pub const BB_RANK_6: Bitboard = BB_RANK_5 << 8; /// The squares on rank 7. pub const BB_RANK_7: Bitboard = BB_RANK_6 << 8; /// The squares on rank 8. pub const BB_RANK_8: Bitboard = BB_RANK_7 << 8; /// The squares on file A. pub const BB_FILE_A: Bitboard = 0x0101010101010101; /// The squares on file B. pub const BB_FILE_B: Bitboard = BB_FILE_A << 1; /// The squares on file C. pub const BB_FILE_C: Bitboard = BB_FILE_B << 1; /// The squares on file D. pub const BB_FILE_D: Bitboard = BB_FILE_C << 1; /// The squares on file E. pub const BB_FILE_E: Bitboard = BB_FILE_D << 1; /// The squares on file F. pub const BB_FILE_F: Bitboard = BB_FILE_E << 1; /// The squares on file G. pub const BB_FILE_G: Bitboard = BB_FILE_F << 1; /// The squares on file H. pub const BB_FILE_H: Bitboard = BB_FILE_G << 1; /// The squares on the main diagonal (A1-H8). pub const BB_MAIN_DIAG: Bitboard = 0x8040201008040201; /// The squares on the main anti-diagonal (H1-A8). pub const BB_MAIN_ANTI_DIAG: Bitboard = 0x0102040810204080; /// Returns the LSB of a value. /// /// The way to calculate this is: `lsb = x & -x;`. /// /// If `x` is `0` this function returns `0`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(lsb(0b10100), 0b100); /// assert_eq!(lsb(0), 0); /// ``` /// ```text /// /// x & -x = lsb(x) /// . . . . . . . . 1 1 1 1 1 1 1 1 . . . . . . . . /// . . 1 . 1 . . . 1 1 . 1 . 1 1 1 . . . . . . . . /// . 1 . . . 1 . . 1 . 1 1 1 . 1 1 . . . . . . . . /// . . . . . . . . 1 1 1 1 1 1 1 1 . . . . . . . . /// . 1 . . . 1 . . & 1 . 1 1 1 . 1 1 = . . . . . . . . /// . . 1 . 1 . . . . . 1 1 . 1 1 1 . . 1 . . . . . /// . . . . . . . . . . . . . . . . . . . . . . . . /// . . . . . . . . . . . . . . . . . . . . . . . . /// ``` #[inline] pub fn lsb(x: Bitboard) -> Bitboard { x & x.wrapping_neg() } /// Resets the LSB of a value to zero. /// /// The way to calculate this is: `x_with_reset_lsb = x & (x - 1);`. /// /// If `*x` is `0` this function does nothing. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// let mut x = 0b100100; /// reset_lsb(&mut x); /// assert_eq!(x, 0b100000); /// reset_lsb(&mut x); /// assert_eq!(x, 0); /// reset_lsb(&mut x); /// assert_eq!(x, 0); /// ``` /// ```text /// /// x & (x - 1) = x_with_reset_lsb(x) /// . . . . . . . . . . . . . . . . . . . . . . . . /// . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . . /// . 1 . . . 1 . . . 1 . . . 1 . . . 1 . . . 1 . . /// . . . . . . . . . . . . . . . . . . . . . . . . /// . 1 . . . 1 . . & . 1 . . . 1 . . = . 1 . . . 1 . . /// . . 1 . 1 . . . 1 1 . . 1 . . . . . . . 1 . . . /// . . . . . . . . 1 1 1 1 1 1 1 1 . . . . . . . . /// . . . . . . . . 1 1 1 1 1 1 1 1 . . . . . . . . /// ``` #[inline] pub fn reset_lsb(x: &mut Bitboard) { *x &= x.wrapping_sub(1); } /// Returns a mask with all bits above the LSB set to `1`. /// /// The way to calculate this is: `above_lsb = x ^ -x;`. /// /// If `x` is `0` this function returns `0`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(above_lsb(0b10100), !0b111); /// assert_eq!(above_lsb(0), 0); /// ``` /// ```text /// /// x ^ -x = above_lsb(x) /// . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// . . 1 . 1 . . . 1 1 . 1 . 1 1 1 1 1 1 1 1 1 1 1 /// . 1 . . . 1 . . 1 . 1 1 1 . 1 1 1 1 1 1 1 1 1 1 /// . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// . 1 . . . 1 . . ^ 1 . 1 1 1 . 1 1 = 1 1 1 1 1 1 1 1 /// . . 1 . 1 . . . . . 1 1 . 1 1 1 . . . 1 1 1 1 1 /// . . . . . . . . . . . . . . . . . . . . . . . . /// . . . . . . . . . . . . . . . . . . . . . . . . /// ``` #[inline] pub fn above_lsb(x: Bitboard) -> Bitboard { x ^ x.wrapping_neg() } /// Returns a mask with all bits below and including the LSB set to /// `1`. /// /// The way to calculate this is: `below_lsb_including = x ^ (x - 1);`. /// /// If `x` is `0` this function returns `0xffffffffffffffff`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(below_lsb_including(0b10100), 0b111); /// assert_eq!(below_lsb_including(0), !0); /// ``` /// ```text /// x ^ (x - 1) = below_lsb_including(x) /// . . . . . . . . . . . . . . . . . . . . . . . . /// . . 1 . 1 . . . . . 1 . 1 . . . . . . . . . . . /// . 1 . . . 1 . . . 1 . . . 1 . . . . . . . . . . /// . . . . . . . . . . . . . . . . . . . . . . . . /// . 1 . . . 1 . . ^ . 1 . . . 1 . . = . . . . . . . . /// . . 1 . 1 . . . 1 1 . . 1 . . . 1 1 1 . . . . . /// . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// ``` #[inline] pub fn below_lsb_including(x: Bitboard) -> Bitboard { x ^ x.wrapping_sub(1) } /// Returns a mask with all bits above and including the LSB set to /// `1`. /// /// The way to calculate this is: `above_lsb_including = x | -x;`. /// /// If `x` is `0` this function returns `0`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(above_lsb_including(0b10100), !0b11); /// assert_eq!(above_lsb_including(0), 0); /// ``` /// ```text /// x | -x = above_lsb_including(x) /// . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// . . 1 . 1 . . . 1 1 . 1 . 1 1 1 1 1 1 1 1 1 1 1 /// . 1 . . . 1 . . 1 . 1 1 1 . 1 1 1 1 1 1 1 1 1 1 /// . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// . 1 . . . 1 . . | 1 . 1 1 1 . 1 1 = 1 1 1 1 1 1 1 1 /// . . 1 . 1 . . . . . 1 1 . 1 1 1 . . 1 1 1 1 1 1 /// . . . . . . . . . . . . . . . . . . . . . . . . /// . . . . . . . . . . . . . . . . . . . . . . . . /// ``` #[inline] pub fn above_lsb_including(x: Bitboard) -> Bitboard { x | x.wrapping_neg() } /// Returns a mask with all bits below the LSB set to `1`. /// /// The way to calculate this is: `below_lsb = !x & (x - 1);`. /// /// If `x` is `0` this function returns `0xffffffffffffffff`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(below_lsb(0b10100), 0b11); /// assert_eq!(below_lsb(0), !0); /// ``` /// ```text /// !x & (x - 1) = below_lsb(x) /// 1 1 1 1 1 1 1 1 . . . . . . . . . . . . . . . . /// 1 1 . 1 . 1 1 1 . . 1 . 1 . . . . . . . . . . . /// 1 . 1 1 1 . 1 1 . 1 . . . 1 . . . . . . . . . . /// 1 1 1 1 1 1 1 1 . . . . . . . . . . . . . . . . /// 1 . 1 1 1 . 1 1 & . 1 . . . 1 . . = . . . . . . . . /// 1 1 . 1 . 1 1 1 1 1 . . 1 . . . 1 1 . . . . . . /// 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /// ``` #[inline] pub fn below_lsb(x: Bitboard) -> Bitboard { !x & x.wrapping_sub(1) } /// Shifts a value with a signed number. /// /// Returns `x << s` if `s` is positive, `x >> s` if `s` is /// negative, `x` if `s` is zero. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(gen_shift(0b101, 1), 0b1010); /// assert_eq!(gen_shift(0b101, -1), 0b10); /// assert_eq!(gen_shift(0b101, 0), 0b101); /// ``` #[inline] pub fn gen_shift(x: Bitboard, s: isize) -> Bitboard { if s > 0 { x << s } else { x >> -s } } /// Returns the binary position of the LSB (bit-scan-forward). /// /// If `x` is `0` this function returns `64`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(bsf(0b100100), 2); /// assert_eq!(bsf(0), 64); /// ``` #[inline] pub fn bsf(x: Bitboard) -> Square { x.trailing_zeros() as Square } /// Returns the binary position of the LSB (bit-scan-forward), and /// resets the LSB to zero. /// /// If `*x` is `0` this function returns `64`. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// let mut x = 0b100100; /// assert_eq!(bsf_reset(&mut x), 2); /// assert_eq!(x, 0b100000); /// assert_eq!(bsf_reset(&mut x), 5); /// assert_eq!(x, 0); /// assert_eq!(bsf_reset(&mut x), 64); /// assert_eq!(x, 0); /// ``` #[inline] pub fn bsf_reset(x: &mut Bitboard) -> Square { let a = lsb(*x); *x ^= a; bsf(a) } /// Returns the number of `1`s in the binary representation of a /// value. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// assert_eq!(pop_count(0b100101), 3); /// assert_eq!(pop_count(0), 0); /// ``` #[inline] pub fn pop_count(b: Bitboard) -> usize { b.count_ones() as usize } /// Returns the set of squares on the same rank as the given square. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// # use alcibiades::squares::*; /// assert_eq!(bb_rank(E4), BB_RANK_4); /// ``` #[inline] pub fn bb_rank(square: Square) -> Bitboard { BB_RANK_1 << ((square >> 3) << 3) } /// Returns the set of squares on the same file as the given square. /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// # use alcibiades::squares::*; /// assert_eq!(bb_file(E4), BB_FILE_E); /// ``` #[inline] pub fn bb_file(square: Square) -> Bitboard { BB_FILE_A << (square % 8) } /// Returns the set of squares on the same diagonal as the given square. /// /// Diagonals go from white's queen-side to black's king-side (A1-H8 /// for example). /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// # use alcibiades::squares::*; /// assert_eq!(bb_diag(D4), BB_MAIN_DIAG); /// ``` #[inline] pub fn bb_diag(square: Square) -> Bitboard { let diag_index = ((square >> 3).wrapping_sub(square % 8)) & 15; if diag_index <= 7 { BB_MAIN_DIAG << (diag_index << 3) } else { BB_MAIN_DIAG >> ((16 - diag_index) << 3) } } /// Returns the set of squares on the same anti-diagonal as the given square. /// /// Anti-diagonals go from white's king-side to black's queen-side /// (H1-A8 for example). /// /// # Examples: /// /// ```rust /// # use alcibiades::bitsets::*; /// # use alcibiades::squares::*; /// assert_eq!(bb_anti_diag(E4), BB_MAIN_ANTI_DIAG); /// ``` #[inline] pub fn bb_anti_diag(square: Square) -> Bitboard { let diag_index = ((square >> 3) + (square % 8)) ^ 7; if diag_index <= 7 { BB_MAIN_ANTI_DIAG >> (diag_index << 3) } else { BB_MAIN_ANTI_DIAG << ((16 - diag_index) << 3) } } #[cfg(test)] mod tests { use super::*; #[test] fn bitsets() { assert_eq!(lsb(0x100100), 0x100); assert_eq!(lsb(0x8000000000000000), 0x8000000000000000); assert_eq!(lsb(0xf800000000000000), 0x0800000000000000); assert_eq!(lsb(0), 0); let mut x = 0x100100u64; reset_lsb(&mut x); assert_eq!(x, 0x100000); reset_lsb(&mut x); assert_eq!(x, 0); reset_lsb(&mut x); assert_eq!(x, 0); assert_eq!(above_lsb(0), 0); assert_eq!(above_lsb(0b11101000), 0xfffffffffffffff0); assert_eq!(above_lsb(0x8000000000000000), 0); assert_eq!(below_lsb_including(0), 0xffffffffffffffff); assert_eq!(below_lsb_including(0b11101000), 0b1111); assert_eq!(below_lsb(0), 0xffffffffffffffff); assert_eq!(below_lsb(0b11101000), 0b111); assert_eq!(above_lsb_including(0), 0); assert_eq!(above_lsb_including(0b1010000), 0xfffffffffffffff0); assert_eq!(above_lsb_including(0x8000000000000000), 0x8000000000000000); assert_eq!(pop_count(0), 0); assert_eq!(pop_count(0b1001101), 4); assert_eq!(pop_count(0xffffffffffffffff), 64); assert_eq!(bsf(0b1001101), 0); assert_eq!(bsf(0b1001000), 3); assert_eq!(bsf(0xf000000000000000), 60); x = 0b1100100; assert_eq!(bsf_reset(&mut x), 2); assert_eq!(x, 0b1100000); } }