overlay-map 0.2.2

A two-layered map data structure for Rust that tracks current and previous values for each key — with zero-clone, in-place state transitions.
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

use criterion::{BatchSize, Criterion, black_box, criterion_group, criterion_main};
use overlay_map::Overlay;

fn bench_push(c: &mut Criterion) {
    let mut group = c.benchmark_group("push");

    group.bench_function("overlay", |b| {
        b.iter_batched(
            || Overlay::new_both(1, 2), // both fg and bg already present
            |mut overlay| {
                black_box(overlay.push(3)); // push evicts fg to bg
            },
            BatchSize::SmallInput,
        );
    });

    group.bench_function("tuple", |b| {
        b.iter_batched(
            || Some((2, Some(1))), // both fg and bg already present
            |mut val| {
                if let Some((fg, bg)) = &mut val {
                    *bg = Some(std::mem::replace(fg, 3)); // same logic: evict fg to bg
                }
                black_box(val);
            },
            BatchSize::SmallInput,
        );
    });

    group.finish();
}

fn bench_pull(c: &mut Criterion) {
    let mut group = c.benchmark_group("pull");

    group.bench_function("overlay", |b| {
        b.iter_batched(
            || Overlay::new_both(1, 2),
            |mut overlay| {
                black_box(overlay.pull());
            },
            BatchSize::SmallInput,
        );
    });

    group.bench_function("tuple", |b| {
        b.iter_batched(
            || Some((2, Some(1))),
            |mut val| {
                let result = if let Some((fg, bg)) = val.as_mut() {
                    let old = *fg;
                    if let Some(new_fg) = bg.take() {
                        *fg = new_fg;
                        Some(old)
                    } else {
                        val = None;
                        Some(old)
                    }
                } else {
                    None
                };
                black_box(val);
                black_box(result);
            },
            BatchSize::SmallInput,
        );
    });

    group.finish();
}

fn bench_swap(c: &mut Criterion) {
    let mut group = c.benchmark_group("swap");

    group.bench_function("overlay", |b| {
        b.iter_batched(
            || Overlay::new_both(1, 2),
            |mut overlay| {
                black_box(overlay.swap(3));
            },
            BatchSize::SmallInput,
        );
    });

    group.bench_function("tuple", |b| {
        b.iter_batched(
            || Some((2, Some(1))),
            |mut val| {
                let result = if let Some((fg, bg)) = &mut val {
                    let old_fg = *fg;
                    let old_bg = bg.replace(old_fg);
                    *fg = 3;
                    old_bg
                } else {
                    val = Some((3, None::<i32>));
                    None
                };
                black_box(val);
                black_box(result);
            },
            BatchSize::SmallInput,
        );
    });

    group.finish();
}

fn bench_flip(c: &mut Criterion) {
    let mut group = c.benchmark_group("flip");

    group.bench_function("overlay", |b| {
        b.iter_batched(
            || Overlay::new_both(1, 2),
            |mut overlay| {
                overlay.flip();
                black_box(overlay);
            },
            BatchSize::SmallInput,
        );
    });

    group.bench_function("tuple", |b| {
        b.iter_batched(
            || Some((1, Some(2))),
            |mut val| {
                if let Some((fg, bg)) = &mut val {
                    if let Some(actual_bg) = bg.take() {
                        std::mem::swap(fg, &mut *bg.get_or_insert(actual_bg));
                    }
                }
                black_box(val);
            },
            BatchSize::SmallInput,
        );
    });

    group.finish();
}

criterion_group!(benches, bench_push, bench_pull, bench_swap, bench_flip);
criterion_main!(benches);