abi_stable_derive/lifetimes/
lifetime_counters.rs

1use super::LifetimeIndex;
2
3use std::fmt::{self, Debug};
4
5/// A set of lifetime indices.
6pub(crate) struct LifetimeCounters {
7    set: Vec<u8>,
8}
9
10const MASK: u8 = 0b11;
11const MAX_VAL: u8 = 3;
12
13impl LifetimeCounters {
14    pub fn new() -> Self {
15        Self { set: Vec::new() }
16    }
17    /// Increments the counter for the `lifetime` lifetime,stopping at 3.
18    pub fn increment(&mut self, lifetime: LifetimeIndex) -> u8 {
19        let (i, shift) = Self::get_index_shift(lifetime.bits);
20        if i >= self.set.len() {
21            self.set.resize(i + 1, 0);
22        }
23        let bits = &mut self.set[i];
24        let mask = MASK << shift;
25        if (*bits & mask) == mask {
26            MAX_VAL
27        } else {
28            *bits += 1 << shift;
29            (*bits >> shift) & MASK
30        }
31    }
32
33    pub fn get(&self, lifetime: LifetimeIndex) -> u8 {
34        let (i, shift) = Self::get_index_shift(lifetime.bits);
35        match self.set.get(i) {
36            Some(&bits) => (bits >> shift) & MASK,
37            None => 0,
38        }
39    }
40
41    fn get_index_shift(lt: usize) -> (usize, u8) {
42        (lt >> 2, ((lt & 3) << 1) as u8)
43    }
44}
45
46impl Debug for LifetimeCounters {
47    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
48        f.debug_list()
49            .entries(self.set.iter().cloned().map(U8Wrapper))
50            .finish()
51    }
52}
53
54#[repr(transparent)]
55struct U8Wrapper(u8);
56
57impl fmt::Debug for U8Wrapper {
58    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
59        fmt::Binary::fmt(&self.0, f)
60    }
61}
62
63#[cfg(test)]
64mod tests {
65    use super::*;
66
67    #[test]
68    fn test_counting() {
69        let mut counters = LifetimeCounters::new();
70
71        let lts = vec![
72            LifetimeIndex::Param(0),
73            LifetimeIndex::Param(1),
74            LifetimeIndex::Param(2),
75            LifetimeIndex::Param(3),
76            LifetimeIndex::Param(4),
77            LifetimeIndex::Param(5),
78            LifetimeIndex::Param(6),
79            LifetimeIndex::Param(7),
80            LifetimeIndex::Param(8),
81            LifetimeIndex::Param(9),
82            LifetimeIndex::Param(999),
83            LifetimeIndex::ANONYMOUS,
84            LifetimeIndex::STATIC,
85            LifetimeIndex::NONE,
86        ];
87
88        for lt in lts {
89            for i in 1..=3 {
90                assert_eq!(counters.get(lt), i - 1);
91                assert_eq!(counters.increment(lt), i);
92                assert_eq!(counters.get(lt), i);
93            }
94        }
95    }
96}
abi_stable_derive/lifetimes/lifetime_counters.rs

abi_stable_derive/lifetimes/
lifetime_counters.rs
