78 lines
2.2 KiB
Rust
78 lines
2.2 KiB
Rust
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/// An efficiently stored array (or set) of bits.
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///
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/// Bits can be set, cleared, or tested by index into the
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/// array of bits. Since the methods are named to follow
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/// the set collection convention you can also think of
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/// it as a set which stores `usize` index values.
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///
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pub struct BitSet {
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blocks: Vec<u64>,
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}
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impl BitSet {
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/// Create a new empty `BitSet`
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pub fn new() -> BitSet {
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BitSet { blocks: Vec::new() }
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}
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/// Removes all entries from the set.
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pub fn clear(&mut self) {
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self.blocks.clear();
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}
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/// Inserts a bit into the set. Sets the entry at `idx` to `true`.
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pub fn insert(&mut self, idx: usize) {
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let (bit,block) = Self::bit_and_block(idx);
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*self.block_mut(block) |= bit;
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}
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/// Removes a bit from the set. Sets the entry at `idx` to `false`.
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pub fn remove(&mut self, idx: usize) {
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let (bit,block) = Self::bit_and_block(idx);
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if self.blocks.len() > block {
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*self.block_mut(block) &= !bit;
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}
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}
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/// Returns the value of the bit at `idx`
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pub fn get(&self, idx: usize) -> bool {
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let (bit,block) = Self::bit_and_block(idx);
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if self.block(block) & bit != 0 {
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return true;
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}
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false
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}
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/// Convert a bit index `idx` into an index into
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/// the block array and the corresponding bit value
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/// inside of that block.
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fn bit_and_block(idx: usize) -> (u64, usize) {
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const SHIFT64: usize = 6;
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const MASK64: usize = (1 << SHIFT64) - 1;
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let bit = (1usize << (idx & MASK64)) as u64;
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let block = idx >> SHIFT64;
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(bit, block)
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}
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/// Returns value stored at index `blk` or returns 0 if `blk`
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/// is index larger than block array.
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fn block(&self, blk: usize) -> u64 {
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if self.blocks.len() > blk {
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self.blocks[blk]
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} else {
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0
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}
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}
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/// Returns mutable reference to value stored at index `blk`
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/// and will resize block vector if index is larger than block
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/// array.
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fn block_mut(&mut self, blk: usize) -> &mut u64 {
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if self.blocks.len() <= blk {
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self.blocks.resize_with(blk + 1, Default::default);
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}
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&mut self.blocks[blk]
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}
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}
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