regex/
sparse.rs

1use std::fmt;
2use std::ops::Deref;
3use std::slice;
4
5/// A sparse set used for representing ordered NFA states.
6///
7/// This supports constant time addition and membership testing. Clearing an
8/// entire set can also be done in constant time. Iteration yields elements
9/// in the order in which they were inserted.
10///
11/// The data structure is based on: https://research.swtch.com/sparse
12/// Note though that we don't actually use uninitialized memory. We generally
13/// reuse allocations, so the initial allocation cost is bareable. However,
14/// its other properties listed above are extremely useful.
15#[derive(Clone)]
16pub struct SparseSet {
17    /// Dense contains the instruction pointers in the order in which they
18    /// were inserted.
19    dense: Vec<usize>,
20    /// Sparse maps instruction pointers to their location in dense.
21    ///
22    /// An instruction pointer is in the set if and only if
23    /// sparse[ip] < dense.len() && ip == dense[sparse[ip]].
24    sparse: Box<[usize]>,
25}
26
27impl SparseSet {
28    pub fn new(size: usize) -> SparseSet {
29        SparseSet {
30            dense: Vec::with_capacity(size),
31            sparse: vec![0; size].into_boxed_slice(),
32        }
33    }
34
35    pub fn len(&self) -> usize {
36        self.dense.len()
37    }
38
39    pub fn is_empty(&self) -> bool {
40        self.dense.is_empty()
41    }
42
43    pub fn capacity(&self) -> usize {
44        self.dense.capacity()
45    }
46
47    pub fn insert(&mut self, value: usize) {
48        let i = self.len();
49        assert!(i < self.capacity());
50        self.dense.push(value);
51        self.sparse[value] = i;
52    }
53
54    pub fn contains(&self, value: usize) -> bool {
55        let i = self.sparse[value];
56        self.dense.get(i) == Some(&value)
57    }
58
59    pub fn clear(&mut self) {
60        self.dense.clear();
61    }
62}
63
64impl fmt::Debug for SparseSet {
65    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
66        write!(f, "SparseSet({:?})", self.dense)
67    }
68}
69
70impl Deref for SparseSet {
71    type Target = [usize];
72
73    fn deref(&self) -> &Self::Target {
74        &self.dense
75    }
76}
77
78impl<'a> IntoIterator for &'a SparseSet {
79    type Item = &'a usize;
80    type IntoIter = slice::Iter<'a, usize>;
81    fn into_iter(self) -> Self::IntoIter {
82        self.iter()
83    }
84}
regex/sparse.rs

regex/
sparse.rs
