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