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//! Utilities to generate bitmasks.
#![doc(hidden)]
/// Generate a bitwise mask for the lower `n` bits.
///
/// # Examples
///
/// ```rust
/// # use minimal_lexical::mask::lower_n_mask;
/// # pub fn main() {
/// assert_eq!(lower_n_mask(2), 0b11);
/// # }
/// ```
#[inline]
pub fn lower_n_mask(n: u64) -> u64 {
debug_assert!(n <= 64, "lower_n_mask() overflow in shl.");
match n == 64 {
// u64::MAX for older Rustc versions.
true => 0xffff_ffff_ffff_ffff,
false => (1 << n) - 1,
}
}
/// Calculate the halfway point for the lower `n` bits.
///
/// # Examples
///
/// ```rust
/// # use minimal_lexical::mask::lower_n_halfway;
/// # pub fn main() {
/// assert_eq!(lower_n_halfway(2), 0b10);
/// # }
/// ```
#[inline]
pub fn lower_n_halfway(n: u64) -> u64 {
debug_assert!(n <= 64, "lower_n_halfway() overflow in shl.");
match n == 0 {
true => 0,
false => nth_bit(n - 1),
}
}
/// Calculate a scalar factor of 2 above the halfway point.
///
/// # Examples
///
/// ```rust
/// # use minimal_lexical::mask::nth_bit;
/// # pub fn main() {
/// assert_eq!(nth_bit(2), 0b100);
/// # }
/// ```
#[inline]
pub fn nth_bit(n: u64) -> u64 {
debug_assert!(n < 64, "nth_bit() overflow in shl.");
1 << n
}
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