ctutils/traits/
ct_gt.rs

1use crate::{Choice, CtLt};
2use core::{
3    cmp,
4    num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU128, NonZeroUsize},
5};
6
7/// Constant time greater than.
8pub trait CtGt {
9    /// Compute whether `self > other` in constant time.
10    #[must_use]
11    fn ct_gt(&self, other: &Self) -> Choice;
12}
13
14// Share the target-specific comparison hardening with `CtLt`.
15macro_rules! impl_unsigned_ct_gt {
16    ( $($uint:ty),+ ) => {
17        $(
18            impl CtGt for $uint {
19                #[inline]
20                fn ct_gt(&self, other: &Self) -> Choice {
21                    other.ct_lt(self)
22                }
23            }
24        )+
25    };
26}
27
28impl_unsigned_ct_gt!(u8, u16, u32, u64, u128, usize);
29
30/// Impl `CtGt` for `NonZero<T>` by calling `NonZero::get`.
31macro_rules! impl_ct_gt_for_nonzero_integer {
32    ( $($ty:ty),+ ) => {
33        $(
34            impl CtGt for $ty {
35                #[inline]
36                fn ct_gt(&self, other: &Self) -> Choice {
37                    self.get().ct_gt(&other.get())
38                }
39            }
40        )+
41    };
42}
43
44impl_ct_gt_for_nonzero_integer!(
45    NonZeroU8,
46    NonZeroU16,
47    NonZeroU32,
48    NonZeroU64,
49    NonZeroU128,
50    NonZeroUsize
51);
52
53impl CtGt for cmp::Ordering {
54    #[inline]
55    #[allow(clippy::arithmetic_side_effects, clippy::cast_sign_loss)]
56    fn ct_gt(&self, other: &Self) -> Choice {
57        let a = (*self as i8) + 1;
58        let b = (*other as i8) + 1;
59
60        // No impl of `CtGt` for `i8`, so use `u8`
61        a.cast_unsigned().ct_gt(&b.cast_unsigned())
62    }
63}
64
65#[cfg(test)]
66mod tests {
67    use super::CtGt;
68    use core::cmp::Ordering;
69
70    /// Test `CtGt`
71    macro_rules! ct_gt_tests {
72         ( $($int:ident),+ ) => {
73             $(
74                mod $int {
75                    use super::CtGt;
76
77                    #[test]
78                    fn ct_gt() {
79                        let a = <$int>::MIN;
80                        let b = <$int>::MAX;
81                        assert!(!a.ct_gt(&a).to_bool());
82                        assert!(!a.ct_gt(&b).to_bool());
83                        assert!(b.ct_gt(&a).to_bool());
84                    }
85
86                }
87             )+
88        };
89    }
90
91    ct_gt_tests!(u8, u16, u32, u64, u128, usize);
92
93    #[test]
94    fn ordering() {
95        assert!(!Ordering::Equal.ct_gt(&Ordering::Equal).to_bool());
96        assert!(!Ordering::Less.ct_gt(&Ordering::Greater).to_bool());
97        assert!(Ordering::Greater.ct_gt(&Ordering::Less).to_bool());
98    }
99}
ctutils/traits/ct_gt.rs

ctutils/traits/
ct_gt.rs
