competitive_hpp/modulo/
utils.rs

1use num::integer::{ExtendedGcd, Integer};
2use num::traits::{PrimInt, Signed};
3
4pub fn mod_inv<A: Copy + Integer + Signed>(a: A, modulo: A) -> A {
5    let ExtendedGcd { x, .. } = a.extended_gcd(&modulo);
6    (modulo + x) % modulo
7}
8
9pub fn mod_pow<A: Copy + Integer + Signed + PrimInt>(x: A, n: A, m: A) -> A {
10    let mut res = A::one();
11    let mut x = x;
12    let mut n = n;
13    while n > A::zero() {
14        if n & A::one() == A::one() {
15            res = (res * x) % m;
16        }
17        x = (x * x) % m;
18        n = n >> 1;
19    }
20    res
21}
22
23#[cfg(test)]
24mod test {
25    use super::*;
26
27    macro_rules! impl_modulo_test(($ty:ty) => {
28        assert_eq!(1, mod_inv(1 as $ty, MOD));
29        assert_eq!(4, mod_inv(2 as $ty, MOD));
30        assert_eq!(5, mod_inv(3 as $ty, MOD));
31        assert_eq!(2, mod_pow(2 as $ty, 4 as $ty, MOD));
32        assert_eq!(1, mod_pow(3 as $ty, 6 as $ty, MOD));
33        assert_eq!(2, mod_pow(5 as $ty, 100 as $ty, MOD));
34        assert_eq!(4, mod_pow(11 as $ty, 1000 as $ty, MOD));
35    });
36
37    #[test]
38    fn test_isize_mod() {
39        const MOD: isize = 7;
40        impl_modulo_test!(isize);
41    }
42
43    #[test]
44    fn test_i64_mod() {
45        const MOD: i64 = 7;
46        impl_modulo_test!(i64);
47    }
48    #[test]
49    fn test_i32_mod() {
50        const MOD: i32 = 7;
51        impl_modulo_test!(i32);
52    }
53}
competitive_hpp/modulo/utils.rs

competitive_hpp/modulo/
utils.rs
