sucds 0.8.3

Succinct data structures in Rust
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

//! Unary iterator on bit vectors.
use super::WORD_LEN;
use crate::bit_vectors::BitVector;
use crate::bit_vectors::NumBits;
use crate::broadword;

/// Iterator for enumerating positions of set bits, created by [`BitVector::unary_iter`].
pub struct UnaryIter<'a> {
    bv: &'a BitVector,
    pos: usize,
    buf: usize,
}

impl<'a> UnaryIter<'a> {
    /// Creates the iterator from the given bit position.
    pub fn new(bv: &'a BitVector, pos: usize) -> Self {
        let buf = bv.words()[pos / WORD_LEN] & (usize::MAX.wrapping_shl((pos % WORD_LEN) as u32));
        Self { bv, pos, buf }
    }

    /// Gets the current bit position.
    #[inline(always)]
    pub const fn position(&self) -> usize {
        self.pos
    }

    /// Skips to the `k`-th one after the current position.
    ///
    /// # Examples
    ///
    /// ```
    /// use sucds::bit_vectors::BitVector;
    ///
    /// let bv = BitVector::from_bits([false, true, false, false, true, true]);
    /// let mut it = bv.unary_iter(0);
    ///
    /// assert_eq!(it.skip1(0), Some(1));
    /// assert_eq!(it.skip1(1), Some(4));
    /// assert_eq!(it.skip1(2), None);
    /// ```
    #[inline(always)]
    pub fn skip1(&mut self, k: usize) -> Option<usize> {
        let mut skipped = 0;
        let mut buf = self.buf;
        loop {
            let w = broadword::popcount(buf);
            if skipped + w > k {
                break;
            }
            skipped += w;
            self.pos += WORD_LEN;
            let word_pos = self.pos / WORD_LEN;
            if self.bv.num_words() <= word_pos {
                return None;
            }
            buf = self.bv.words()[word_pos];
        }
        debug_assert!(buf != 0);
        let pos_in_word = broadword::select_in_word(buf, k - skipped).unwrap();
        self.buf = buf & usize::MAX.wrapping_shl(pos_in_word as u32);
        self.pos = (self.pos & !(WORD_LEN - 1)) + pos_in_word;
        Some(self.pos)
    }

    /// Skips to the `k`-th zero after the current position.
    ///
    /// # Examples
    ///
    /// ```
    /// use sucds::bit_vectors::BitVector;
    ///
    /// let bv = BitVector::from_bits([false, true, false, false, true, true]);
    /// let mut it = bv.unary_iter(0);
    ///
    /// assert_eq!(it.skip0(0), Some(0));
    /// assert_eq!(it.skip0(1), Some(2));
    /// assert_eq!(it.skip0(2), None);
    /// ```
    #[inline(always)]
    pub fn skip0(&mut self, k: usize) -> Option<usize> {
        let mut skipped = 0;
        let pos_in_word = self.pos % WORD_LEN;
        let mut buf = !self.buf & usize::MAX.wrapping_shl(pos_in_word as u32);
        loop {
            let w = broadword::popcount(buf);
            if skipped + w > k {
                break;
            }
            skipped += w;
            self.pos += WORD_LEN;
            let word_pos = self.pos / WORD_LEN;
            if self.bv.num_words() <= word_pos {
                return None;
            }
            buf = !self.bv.words()[word_pos];
        }
        debug_assert!(buf != 0);
        let pos_in_word = broadword::select_in_word(buf, k - skipped).unwrap();
        self.buf = !buf & usize::MAX.wrapping_shl(pos_in_word as u32);
        self.pos = (self.pos & !(WORD_LEN - 1)) + pos_in_word;
        Some(self.pos).filter(|&x| x < self.bv.num_bits())
    }
}

impl Iterator for UnaryIter<'_> {
    type Item = usize;

    #[inline(always)]
    fn next(&mut self) -> Option<Self::Item> {
        let mut buf = self.buf;
        while buf == 0 {
            self.pos += WORD_LEN;
            let word_pos = self.pos / WORD_LEN;
            if self.bv.num_words() <= word_pos {
                return None;
            }
            buf = self.bv.words()[word_pos];
        }
        let pos_in_word = broadword::lsb(buf).unwrap();
        self.buf = buf & (buf - 1); // clear LSB
        self.pos = (self.pos & !(WORD_LEN - 1)) + pos_in_word;
        Some(self.pos)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_next_all_zeros() {
        let bv = BitVector::from_bit(false, 100);
        let mut it = bv.unary_iter(0);
        assert_eq!(it.next(), None);
    }

    #[test]
    fn test_skip1_all_zeros() {
        let bv = BitVector::from_bit(false, 100);
        let mut it = bv.unary_iter(0);
        assert_eq!(it.skip1(0), None);
    }

    #[test]
    fn test_skip0_all_ones() {
        let bv = BitVector::from_bit(true, 100);
        let mut it = bv.unary_iter(0);
        assert_eq!(it.skip0(0), None);
    }
}