1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151

use super::Bits;
use storage::{BlockType, Address};

/// Mutable bit vector operations that don’t affect the length.
///
/// Minimal complete definition is `set_bit` or `set_block`, since each
/// is defined in terms of the other. Note that `set_block` in terms of
/// `set_bit` is inefficient, and thus you should implement `set_block`
/// directly if possible.
pub trait BitsMut: Bits {
    /// Sets the bit at `position` to `value`.
    ///
    /// The default implementation uses `get_raw_block` and `set_block`.
    ///
    /// # Panics
    ///
    /// Panics if `position` is out of bounds.
    fn set_bit(&mut self, position: u64, value: bool) {
        assert!(position < self.bit_len(), "BitsMut::set_bit: out of bounds");

        let address = Address::new::<Self::Block>(position);
        let old_block = self.get_raw_block(address.block_index);
        let new_block = old_block.with_bit(address.bit_offset, value);
        self.set_block(address.block_index, new_block);
    }

    /// Sets the block at `position` to `value`.
    ///
    /// The bits are laid out `Block::nbits()` per block, with the notional
    /// zeroth bit in the least significant position. If `self.bit_len()` is
    /// not a multiple of `Block::nbits()` then the last block will
    /// contain extra bits that are not part of the bit vector. Implementations
    /// of `set_block` should not change those trailing bits.
    ///
    /// The default implementation sets a block by setting each of its bits
    /// in turn. Consider it a slow reference implementation, and override it.
    ///
    /// # Panics
    ///
    /// Panics if `position` is out of bounds.
    fn set_block(&mut self, position: usize, mut value: Self::Block) {
        let offset = Self::Block::mul_nbits(position);
        let count  = Self::Block::block_bits(self.bit_len(), position);

        for i in 0 .. count as u64 {
            let bit = value & Self::Block::one() != Self::Block::zero();
            self.set_bit(offset + i, bit);
            value = value >> 1;
        }
    }

    /// Sets `count` bits starting at bit index `start`, interpreted as a
    /// little-endian integer.
    ///
    /// # Panics
    ///
    /// Panics if the bit span goes out of bounds.
    fn set_bits(&mut self, start: u64, count: usize, value: Self::Block) {
        let limit = start + count as u64;
        assert!(limit <= self.bit_len(), "BitsMut::set_bits: out of bounds");

        let address = Address::new::<Self::Block>(start);
        let margin = Self::Block::nbits() - address.bit_offset;

        if margin >= count {
            let old_block = self.get_raw_block(address.block_index);
            let new_block = old_block.with_bits(address.bit_offset, count, value);
            self.set_block(address.block_index, new_block);
            return;
        }

        let extra = count - margin;

        let old_block1 = self.get_raw_block(address.block_index);
        let old_block2 = self.get_raw_block(address.block_index + 1);

        let high_bits = value >> margin;

        let new_block1 = old_block1.with_bits(address.bit_offset,
                                              margin, value);
        let new_block2 = old_block2.with_bits(0, extra, high_bits);
        self.set_block(address.block_index, new_block1);
        self.set_block(address.block_index + 1, new_block2);
    }
}

impl<'a, T: BitsMut + ?Sized> BitsMut for &'a mut T {
    fn set_bit(&mut self, position: u64, value: bool) {
        T::set_bit(*self, position, value);
    }

    fn set_block(&mut self, position: usize, value: Self::Block) {
        T::set_block(*self, position, value);
    }

    fn set_bits(&mut self, start: u64, count: usize, value: Self::Block) {
        T::set_bits(*self, start, count, value);
    }
}

impl<Block: BlockType> BitsMut for Box<dyn BitsMut<Block = Block>> {
    fn set_bit(&mut self, position: u64, value: bool) {
        (**self).set_bit(position, value);
    }

    fn set_block(&mut self, position: usize, value: Block) {
        (**self).set_block(position, value);
    }

    fn set_bits(&mut self, start: u64, len: usize, value: Block) {
        (**self).set_bits(start, len, value);
    }
}

impl<Block: BlockType> BitsMut for [Block] {
    fn set_bit(&mut self, position: u64, value: bool) {
        let address = Address::new::<Block>(position);
        let block = &mut self[address.block_index];
        *block = block.with_bit(address.bit_offset, value);
    }

    fn set_block(&mut self, position: usize, value: Block) {
        self[position] = value;
    }
}

impl<Block: BlockType> BitsMut for Vec<Block> {
    fn set_bit(&mut self, position: u64, value: bool) {
        <[Block]>::set_bit(&mut *self, position, value);
    }

    fn set_block(&mut self, position: usize, value: Block) {
        <[Block]>::set_block(&mut *self, position, value);
    }
}

impl BitsMut for [bool] {
    fn set_bit(&mut self, position: u64, value: bool) {
        let position = position.to_usize()
            .expect("Vec<bool>::set_bit: overflow");
        self[position] = value;
    }
}

impl BitsMut for Vec<bool> {
    #[inline]
    fn set_bit(&mut self, position: u64, value: bool) {
        self.as_mut_slice().set_bit(position, value)
    }
}