| //! 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 |
| } |
