bit_field/lib.rs
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//! Provides the abstraction of a bit field, which allows for bit-level update and retrieval
//! operations.
#![no_std]
#[cfg(test)]
mod tests;
use core::ops::{Bound, Range, RangeBounds};
/// A generic trait which provides methods for extracting and setting specific bits or ranges of
/// bits.
pub trait BitField {
/// The number of bits in this bit field.
///
/// ```rust
/// use bit_field::BitField;
///
/// assert_eq!(u32::BIT_LENGTH, 32);
/// assert_eq!(u64::BIT_LENGTH, 64);
/// ```
const BIT_LENGTH: usize;
/// Obtains the bit at the index `bit`; note that index 0 is the least significant bit, while
/// index `length() - 1` is the most significant bit.
///
/// ```rust
/// use bit_field::BitField;
///
/// let value: u32 = 0b110101;
///
/// assert_eq!(value.get_bit(1), false);
/// assert_eq!(value.get_bit(2), true);
/// ```
///
/// ## Panics
///
/// This method will panic if the bit index is out of bounds of the bit field.
fn get_bit(&self, bit: usize) -> bool;
/// Obtains the range of bits specified by `range`; note that index 0 is the least significant
/// bit, while index `length() - 1` is the most significant bit.
///
/// ```rust
/// use bit_field::BitField;
///
/// let value: u32 = 0b110101;
///
/// assert_eq!(value.get_bits(0..3), 0b101);
/// assert_eq!(value.get_bits(2..6), 0b1101);
/// assert_eq!(value.get_bits(..), 0b110101);
/// assert_eq!(value.get_bits(3..=3), value.get_bit(3) as u32);
/// ```
///
/// ## Panics
///
/// This method will panic if the start or end indexes of the range are out of bounds of the
/// bit field.
fn get_bits<T: RangeBounds<usize>>(&self, range: T) -> Self;
/// Sets the bit at the index `bit` to the value `value` (where true means a value of '1' and
/// false means a value of '0'); note that index 0 is the least significant bit, while index
/// `length() - 1` is the most significant bit.
///
/// ```rust
/// use bit_field::BitField;
///
/// let mut value = 0u32;
///
/// value.set_bit(1, true);
/// assert_eq!(value, 2u32);
///
/// value.set_bit(3, true);
/// assert_eq!(value, 10u32);
///
/// value.set_bit(1, false);
/// assert_eq!(value, 8u32);
/// ```
///
/// ## Panics
///
/// This method will panic if the bit index is out of the bounds of the bit field.
fn set_bit(&mut self, bit: usize, value: bool) -> &mut Self;
/// Sets the range of bits defined by the range `range` to the lower bits of `value`; to be
/// specific, if the range is N bits long, the N lower bits of `value` will be used; if any of
/// the other bits in `value` are set to 1, this function will panic.
///
/// ```rust
/// use bit_field::BitField;
///
/// let mut value = 0u32;
///
/// value.set_bits(0..2, 0b11);
/// assert_eq!(value, 0b11);
///
/// value.set_bits(2..=3, 0b11);
/// assert_eq!(value, 0b1111);
///
/// value.set_bits(..4, 0b1010);
/// assert_eq!(value, 0b1010);
/// ```
///
/// ## Panics
///
/// This method will panic if the range is out of bounds of the bit field, or if there are `1`s
/// not in the lower N bits of `value`.
fn set_bits<T: RangeBounds<usize>>(&mut self, range: T, value: Self) -> &mut Self;
}
pub trait BitArray<T: BitField> {
/// Returns the length, eg number of bits, in this bit array.
///
/// ```rust
/// use bit_field::BitArray;
///
/// assert_eq!([0u8, 4u8, 8u8].bit_length(), 24);
/// assert_eq!([0u32, 5u32].bit_length(), 64);
/// ```
fn bit_length(&self) -> usize;
/// Obtains the bit at the index `bit`; note that index 0 is the least significant bit, while
/// index `length() - 1` is the most significant bit.
///
/// ```rust
/// use bit_field::BitArray;
///
/// let value: [u32; 1] = [0b110101];
///
/// assert_eq!(value.get_bit(1), false);
/// assert_eq!(value.get_bit(2), true);
/// ```
///
/// ## Panics
///
/// This method will panic if the bit index is out of bounds of the bit array.
fn get_bit(&self, bit: usize) -> bool;
/// Obtains the range of bits specified by `range`; note that index 0 is the least significant
/// bit, while index `length() - 1` is the most significant bit.
///
/// ```rust
/// use bit_field::BitArray;
///
/// let value: [u32; 2] = [0b110101, 0b11];
///
/// assert_eq!(value.get_bits(0..3), 0b101);
/// assert_eq!(value.get_bits(..6), 0b110101);
/// assert_eq!(value.get_bits(31..33), 0b10);
/// assert_eq!(value.get_bits(5..=32), 0b1_0000_0000_0000_0000_0000_0000_001);
/// assert_eq!(value.get_bits(34..), 0);
/// ```
///
/// ## Panics
///
/// This method will panic if the start or end indexes of the range are out of bounds of the
/// bit array, or if the range can't be contained by the bit field T.
fn get_bits<U: RangeBounds<usize>>(&self, range: U) -> T;
/// Sets the bit at the index `bit` to the value `value` (where true means a value of '1' and
/// false means a value of '0'); note that index 0 is the least significant bit, while index
/// `length() - 1` is the most significant bit.
///
/// ```rust
/// use bit_field::BitArray;
///
/// let mut value = [0u32];
///
/// value.set_bit(1, true);
/// assert_eq!(value, [2u32]);
///
/// value.set_bit(3, true);
/// assert_eq!(value, [10u32]);
///
/// value.set_bit(1, false);
/// assert_eq!(value, [8u32]);
/// ```
///
/// ## Panics
///
/// This method will panic if the bit index is out of the bounds of the bit array.
fn set_bit(&mut self, bit: usize, value: bool);
/// Sets the range of bits defined by the range `range` to the lower bits of `value`; to be
/// specific, if the range is N bits long, the N lower bits of `value` will be used; if any of
/// the other bits in `value` are set to 1, this function will panic.
///
/// ```rust
/// use bit_field::BitArray;
///
/// let mut value = [0u32, 0u32];
///
/// value.set_bits(0..2, 0b11);
/// assert_eq!(value, [0b11, 0u32]);
///
/// value.set_bits(31..35, 0b1010);
/// assert_eq!(value, [0x0003, 0b101]);
/// ```
///
/// ## Panics
///
/// This method will panic if the range is out of bounds of the bit array,
/// if the range can't be contained by the bit field T, or if there are `1`s
/// not in the lower N bits of `value`.
fn set_bits<U: RangeBounds<usize>>(&mut self, range: U, value: T);
}
/// An internal macro used for implementing BitField on the standard integral types.
macro_rules! bitfield_numeric_impl {
($($t:ty)*) => ($(
impl BitField for $t {
const BIT_LENGTH: usize = ::core::mem::size_of::<Self>() as usize * 8;
#[track_caller]
#[inline]
fn get_bit(&self, bit: usize) -> bool {
assert!(bit < Self::BIT_LENGTH);
(*self & (1 << bit)) != 0
}
#[track_caller]
#[inline]
fn get_bits<T: RangeBounds<usize>>(&self, range: T) -> Self {
let range = to_regular_range(&range, Self::BIT_LENGTH);
assert!(range.start < Self::BIT_LENGTH);
assert!(range.end <= Self::BIT_LENGTH);
assert!(range.start < range.end);
// shift away high bits
let bits = *self << (Self::BIT_LENGTH - range.end) >> (Self::BIT_LENGTH - range.end);
// shift away low bits
bits >> range.start
}
#[track_caller]
#[inline]
fn set_bit(&mut self, bit: usize, value: bool) -> &mut Self {
assert!(bit < Self::BIT_LENGTH);
if value {
*self |= 1 << bit;
} else {
*self &= !(1 << bit);
}
self
}
#[track_caller]
#[inline]
fn set_bits<T: RangeBounds<usize>>(&mut self, range: T, value: Self) -> &mut Self {
let range = to_regular_range(&range, Self::BIT_LENGTH);
assert!(range.start < Self::BIT_LENGTH);
assert!(range.end <= Self::BIT_LENGTH);
assert!(range.start < range.end);
assert!(value << (Self::BIT_LENGTH - (range.end - range.start)) >>
(Self::BIT_LENGTH - (range.end - range.start)) == value,
"value does not fit into bit range");
let bitmask: Self = !(!0 << (Self::BIT_LENGTH - range.end) >>
(Self::BIT_LENGTH - range.end) >>
range.start << range.start);
// set bits
*self = (*self & bitmask) | (value << range.start);
self
}
}
)*)
}
bitfield_numeric_impl! { u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize }
impl<T: BitField> BitArray<T> for [T] {
#[inline]
fn bit_length(&self) -> usize {
self.len() * T::BIT_LENGTH
}
#[track_caller]
#[inline]
fn get_bit(&self, bit: usize) -> bool {
let slice_index = bit / T::BIT_LENGTH;
let bit_index = bit % T::BIT_LENGTH;
self[slice_index].get_bit(bit_index)
}
#[track_caller]
#[inline]
fn get_bits<U: RangeBounds<usize>>(&self, range: U) -> T {
let range = to_regular_range(&range, self.bit_length());
assert!(range.len() <= T::BIT_LENGTH);
let slice_start = range.start / T::BIT_LENGTH;
let slice_end = range.end / T::BIT_LENGTH;
let bit_start = range.start % T::BIT_LENGTH;
let bit_end = range.end % T::BIT_LENGTH;
let len = range.len();
assert!(slice_end - slice_start <= 1);
if slice_start == slice_end {
self[slice_start].get_bits(bit_start..bit_end)
} else if bit_end == 0 {
self[slice_start].get_bits(bit_start..T::BIT_LENGTH)
} else {
let mut ret = self[slice_start].get_bits(bit_start..T::BIT_LENGTH);
ret.set_bits(
(T::BIT_LENGTH - bit_start)..len,
self[slice_end].get_bits(0..bit_end),
);
ret
}
}
#[track_caller]
#[inline]
fn set_bit(&mut self, bit: usize, value: bool) {
let slice_index = bit / T::BIT_LENGTH;
let bit_index = bit % T::BIT_LENGTH;
self[slice_index].set_bit(bit_index, value);
}
#[track_caller]
#[inline]
fn set_bits<U: RangeBounds<usize>>(&mut self, range: U, value: T) {
let range = to_regular_range(&range, self.bit_length());
assert!(range.len() <= T::BIT_LENGTH);
let slice_start = range.start / T::BIT_LENGTH;
let slice_end = range.end / T::BIT_LENGTH;
let bit_start = range.start % T::BIT_LENGTH;
let bit_end = range.end % T::BIT_LENGTH;
assert!(slice_end - slice_start <= 1);
if slice_start == slice_end {
self[slice_start].set_bits(bit_start..bit_end, value);
} else if bit_end == 0 {
self[slice_start].set_bits(bit_start..T::BIT_LENGTH, value);
} else {
self[slice_start].set_bits(
bit_start..T::BIT_LENGTH,
value.get_bits(0..T::BIT_LENGTH - bit_start),
);
self[slice_end].set_bits(
0..bit_end,
value.get_bits(T::BIT_LENGTH - bit_start..T::BIT_LENGTH),
);
}
}
}
fn to_regular_range<T: RangeBounds<usize>>(generic_rage: &T, bit_length: usize) -> Range<usize> {
let start = match generic_rage.start_bound() {
Bound::Excluded(&value) => value + 1,
Bound::Included(&value) => value,
Bound::Unbounded => 0,
};
let end = match generic_rage.end_bound() {
Bound::Excluded(&value) => value,
Bound::Included(&value) => value + 1,
Bound::Unbounded => bit_length,
};
start..end
}