//! Utilities to generate bitmasks.

#![doc(hidden)]

/// Generate a bitwise mask for the lower `n` bits.

///

/// # Examples

///

/// ```rust

/// # use lexical_parse_float::mask::lower_n_mask;

/// assert_eq!(lower_n_mask(2), 0b11);

/// ```

#[must_use]

#[inline(always)]

#[allow(clippy::match_bool)] // reason="easier to visualize logic"

pub const fn lower_n_mask(n: u64) -> u64 {

    debug_assert!(n <= 64, "lower_n_mask() overflow in shl.");

    match n == 64 {

        true => u64::MAX,

        false => (1 << n) - 1,

    }

}

/// Calculate the halfway point for the lower `n` bits.

///

/// # Examples

///

/// ```rust

/// # use lexical_parse_float::mask::lower_n_halfway;

/// assert_eq!(lower_n_halfway(2), 0b10);

/// ```

#[must_use]

#[inline(always)]

#[allow(clippy::match_bool)] // reason="easier to visualize logic"

pub const 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 lexical_parse_float::mask::nth_bit;

/// assert_eq!(nth_bit(2), 0b100);

/// ```

#[must_use]

#[inline(always)]

pub const fn nth_bit(n: u64) -> u64 {

    debug_assert!(n < 64, "nth_bit() overflow in shl.");

    1 << n

}