60 lines
2.1 KiB
Rust
60 lines
2.1 KiB
Rust
// Copyright 2016 Brian Smith.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
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// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
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// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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use crate::error;
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#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd)]
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pub struct BitLength(usize);
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// Lengths measured in bits, where all arithmetic is guaranteed not to
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// overflow.
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impl BitLength {
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#[inline]
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pub const fn from_usize_bits(bits: usize) -> BitLength { BitLength(bits) }
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#[inline]
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pub fn from_usize_bytes(bytes: usize) -> Result<BitLength, error::Unspecified> {
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let bits = bytes.checked_mul(8).ok_or(error::Unspecified)?;
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Ok(BitLength::from_usize_bits(bits))
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}
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#[inline]
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pub fn half_rounded_up(&self) -> BitLength {
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let round_up = self.0 & 1;
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BitLength((self.0 / 2) + round_up)
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}
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#[inline]
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pub fn as_usize_bits(&self) -> usize { self.0 }
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#[inline]
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pub fn as_usize_bytes_rounded_up(&self) -> usize {
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// Equivalent to (self.0 + 7) / 8, except with no potential for
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// overflow and without branches.
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// Branchless round_up = if self.0 & 0b111 != 0 { 1 } else { 0 };
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let round_up = ((self.0 >> 2) | (self.0 >> 1) | self.0) & 1;
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(self.0 / 8) + round_up
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}
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#[inline]
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pub fn try_sub(self, other: BitLength) -> Result<BitLength, error::Unspecified> {
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let sum = self.0.checked_sub(other.0).ok_or(error::Unspecified)?;
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Ok(BitLength(sum))
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}
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}
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pub const ONE: BitLength = BitLength(1);
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