Sha256: ce68628eeb395fd340e5d34f726b92f8a4686a96e9264c47809f805e8c8546f7
Contents?: true
Size: 1.67 KB
Versions: 5
Compression:
Stored size: 1.67 KB
Contents
use std::fmt;
#[derive(Clone, Copy, PartialEq)]
pub(crate) struct Pack {
mask: usize,
shift: u32,
}
impl Pack {
/// Value is packed in the `width` least-significant bits.
pub(crate) const fn least_significant(width: u32) -> Pack {
let mask = mask_for(width);
Pack { mask, shift: 0 }
}
/// Value is packed in the `width` more-significant bits.
pub(crate) const fn then(&self, width: u32) -> Pack {
let shift = usize::BITS - self.mask.leading_zeros();
let mask = mask_for(width) << shift;
Pack { mask, shift }
}
/// Width, in bits, dedicated to storing the value.
pub(crate) const fn width(&self) -> u32 {
usize::BITS - (self.mask >> self.shift).leading_zeros()
}
/// Max representable value.
pub(crate) const fn max_value(&self) -> usize {
(1 << self.width()) - 1
}
pub(crate) fn pack(&self, value: usize, base: usize) -> usize {
assert!(value <= self.max_value());
(base & !self.mask) | (value << self.shift)
}
pub(crate) fn unpack(&self, src: usize) -> usize {
unpack(src, self.mask, self.shift)
}
}
impl fmt::Debug for Pack {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(
fmt,
"Pack {{ mask: {:b}, shift: {} }}",
self.mask, self.shift
)
}
}
/// Returns a `usize` with the right-most `n` bits set.
pub(crate) const fn mask_for(n: u32) -> usize {
let shift = 1usize.wrapping_shl(n - 1);
shift | (shift - 1)
}
/// Unpacks a value using a mask & shift.
pub(crate) const fn unpack(src: usize, mask: usize, shift: u32) -> usize {
(src & mask) >> shift
}
Version data entries
5 entries across 5 versions & 1 rubygems