1 // Copyright 2016 Brian Smith. 2 // 3 // Permission to use, copy, modify, and/or distribute this software for any 4 // purpose with or without fee is hereby granted, provided that the above 5 // copyright notice and this permission notice appear in all copies. 6 // 7 // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES 8 // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 9 // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY 10 // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 11 // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 12 // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 13 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 14 15 //! Bit Lengths. 16 17 use crate::error; 18 19 /// A length of an integer value, measured in bits. 20 #[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd)] 21 pub struct BitLength(usize); 22 23 impl BitLength { 24 /// Constructs a `BitLength` from `bits`, where bits is interpreted as a bit length. 25 #[inline] from_usize_bits(bits: usize) -> Self26 pub const fn from_usize_bits(bits: usize) -> Self { 27 Self(bits) 28 } 29 30 /// Constructs a `BitLength` from `bits`, where bits is interpreted as a byte length. 31 #[inline] from_usize_bytes(bytes: usize) -> Result<Self, error::Unspecified>32 pub fn from_usize_bytes(bytes: usize) -> Result<Self, error::Unspecified> { 33 let bits = bytes.checked_mul(8).ok_or(error::Unspecified)?; 34 Ok(Self::from_usize_bits(bits)) 35 } 36 37 #[cfg(feature = "alloc")] 38 #[inline] half_rounded_up(&self) -> Self39 pub(crate) fn half_rounded_up(&self) -> Self { 40 let round_up = self.0 & 1; 41 Self((self.0 / 2) + round_up) 42 } 43 44 #[inline] as_usize_bits(&self) -> usize45 pub(crate) fn as_usize_bits(&self) -> usize { 46 self.0 47 } 48 49 #[cfg(feature = "alloc")] 50 #[inline] as_usize_bytes_rounded_up(&self) -> usize51 pub(crate) const fn as_usize_bytes_rounded_up(&self) -> usize { 52 // Equivalent to (self.0 + 7) / 8, except with no potential for 53 // overflow and without branches. 54 55 // Branchless round_up = if self.0 & 0b111 != 0 { 1 } else { 0 }; 56 let round_up = ((self.0 >> 2) | (self.0 >> 1) | self.0) & 1; 57 58 (self.0 / 8) + round_up 59 } 60 61 #[cfg(feature = "alloc")] 62 #[inline] try_sub_1(self) -> Result<Self, error::Unspecified>63 pub(crate) fn try_sub_1(self) -> Result<Self, error::Unspecified> { 64 let sum = self.0.checked_sub(1).ok_or(error::Unspecified)?; 65 Ok(Self(sum)) 66 } 67 } 68