succinct 0.5.2

Succinct data structures for Rust
Documentation 
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
152
153
154
155
156

use num_traits::PrimInt;

/// Averages two `PrimInt`s without overflowing.
pub fn average<P: PrimInt>(x: P, y: P) -> P {
    let almost_average = (x >> 1) + (y >> 1);
    let extra_bit = (x & P::one()) + (y & P::one()) >> 1;

    almost_average + extra_bit
}

/// Finds the smallest `d: D` in the interval `start .. limit` such
/// that `f(d) >= value`; requires that `f` be monotonically
/// non-decreasing.
///
/// Does not call `f` on `D`s outside the specified interval.
pub fn binary_search_function<D, R, F>(
    mut start: D, mut limit: D, value: R, f: F) -> Option<D>
        where D: PrimInt,
              R: Ord,
              F: Fn(D) -> R {

    if start >= limit { return None; }
    if f(start) >= value { return Some(start); }

    // Now we know the answer isn't `start`, which means for every
    // candidate `mid`, `mid - 1` will still be in the domain of `f`.
    start = start + D::one();

    while start < limit {
        let mid = average(start, limit);

        if f(mid) >= value {
            if f(mid - D::one()) < value {
                return Some(mid);
            } else {
                limit = mid;
            }
        } else {
            start = mid + D::one();
        }
    }

    None
}


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

    #[test]
    fn avg_2_4() {
        assert_eq!(3, average(2, 4));
    }

    #[test]
    fn avg_2_5() {
        assert_eq!(3, average(2, 5));
    }

    #[test]
    fn avg_3_4() {
        assert_eq!(3, average(3, 4));
    }

    #[test]
    fn avg_3_5() {
        assert_eq!(4, average(3, 5));
    }

    #[test]
    fn avg_big() {
        let big: usize = !0;
        assert_eq!(big - 1, average(big, big - 1));
        assert_eq!(big - 1, average(big, big - 2));
        assert_eq!(big - 1, average(big - 1, big - 1));
        assert_eq!(big - 2, average(big - 2, big - 1));
        assert_eq!(big - 2, average(big - 2, big - 2));
        assert_eq!(big - 2, average(big - 1, big - 3));
    }

    fn search_slice(value: usize, slice: &[usize])
                    -> Option<usize> {
        binary_search_function(0, slice.len(), value, |index| slice[index])
    }

    const MAX_LEN: usize = 32;

    #[test]
    fn binary_search_01() {
        let mut vec = Vec::<usize>::with_capacity(MAX_LEN);

        for len in 0 .. MAX_LEN + 1 {
            for result in 0 .. len {
                vec.clear();
                for _ in 0 .. result { vec.push(0); }
                for _ in result .. len { vec.push(1); }
                assert_eq!(Some(result), search_slice(1, &vec));
            }

            vec.clear();
            for _ in 0 .. len { vec.push(0) }
            assert_eq!(None, search_slice(1, &vec));
        }
    }

    #[test]
    fn binary_search_02() {
        let mut vec = Vec::<usize>::with_capacity(MAX_LEN);

        for len in 0 .. MAX_LEN + 1 {
            for result in 0 .. len {
                vec.clear();
                for _ in 0 .. result { vec.push(0); }
                for _ in result .. len { vec.push(2); }
                assert_eq!(Some(result), search_slice(1, &vec));
            }

            vec.clear();
            for _ in 0 .. len { vec.push(0) }
            assert_eq!(None, search_slice(1, &vec));
        }
    }

    #[test]
    fn binary_search_iota() {
        let mut vec = Vec::<usize>::with_capacity(MAX_LEN);

        for len in 0 .. MAX_LEN + 1 {
            vec.clear();
            for i in 0 .. len { vec.push(i); }

            for i in 0 .. len {
                assert_eq!(Some(i), search_slice(i, &vec));
            }

            assert_eq!(None, search_slice(len, &vec));
        }
    }

    // #[test]
    // fn binary_search_2iota() {
    //     let mut vec = Vec::<usize>::with_capacity(MAX_LEN);

    //     for len in 0 .. MAX_LEN + 1 {
    //         vec.clear();
    //         for i in 0 .. len { vec.push(2 * i); }

    //         // assert_eq!(Some(0), search_slice(0, &vec));
    //         for i in 1 .. len {
    //             assert_eq!(Some(i), search_slice(2 * i, &vec));
    //             assert_eq!(Some(i), search_slice(2 * i - 1, &vec));
    //         }
    //     }
    // }
}