crypto_bigint/uint/modular/constant_mod/
const_sub.rs

1use core::ops::{Sub, SubAssign};
2
3use crate::modular::sub::sub_montgomery_form;
4
5use super::{Residue, ResidueParams};
6
7impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Residue<MOD, LIMBS> {
8    /// Subtracts `rhs`.
9    pub const fn sub(&self, rhs: &Self) -> Self {
10        Self {
11            montgomery_form: sub_montgomery_form(
12                &self.montgomery_form,
13                &rhs.montgomery_form,
14                &MOD::MODULUS,
15            ),
16            phantom: core::marker::PhantomData,
17        }
18    }
19}
20
21impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<&Residue<MOD, LIMBS>>
22    for &Residue<MOD, LIMBS>
23{
24    type Output = Residue<MOD, LIMBS>;
25    fn sub(self, rhs: &Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
26        self.sub(rhs)
27    }
28}
29
30impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<Residue<MOD, LIMBS>>
31    for &Residue<MOD, LIMBS>
32{
33    type Output = Residue<MOD, LIMBS>;
34    #[allow(clippy::op_ref)]
35    fn sub(self, rhs: Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
36        self - &rhs
37    }
38}
39
40impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<&Residue<MOD, LIMBS>>
41    for Residue<MOD, LIMBS>
42{
43    type Output = Residue<MOD, LIMBS>;
44    #[allow(clippy::op_ref)]
45    fn sub(self, rhs: &Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
46        &self - rhs
47    }
48}
49
50impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<Residue<MOD, LIMBS>>
51    for Residue<MOD, LIMBS>
52{
53    type Output = Residue<MOD, LIMBS>;
54    fn sub(self, rhs: Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
55        &self - &rhs
56    }
57}
58
59impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> SubAssign<&Self> for Residue<MOD, LIMBS> {
60    fn sub_assign(&mut self, rhs: &Self) {
61        *self = *self - rhs;
62    }
63}
64
65impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> SubAssign<Self> for Residue<MOD, LIMBS> {
66    fn sub_assign(&mut self, rhs: Self) {
67        *self -= &rhs;
68    }
69}
70
71#[cfg(test)]
72mod tests {
73    use crate::{const_residue, impl_modulus, modular::constant_mod::ResidueParams, U256};
74
75    impl_modulus!(
76        Modulus,
77        U256,
78        "ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551"
79    );
80
81    #[test]
82    fn sub_overflow() {
83        let x =
84            U256::from_be_hex("44acf6b7e36c1342c2c5897204fe09504e1e2efb1a900377dbc4e7a6a133ec56");
85        let mut x_mod = const_residue!(x, Modulus);
86
87        let y =
88            U256::from_be_hex("d5777c45019673125ad240f83094d4252d829516fac8601ed01979ec1ec1a251");
89        let y_mod = const_residue!(y, Modulus);
90
91        x_mod -= &y_mod;
92
93        let expected =
94            U256::from_be_hex("6f357a71e1d5a03167f34879d469352add829491c6df41ddff65387d7ed56f56");
95
96        assert_eq!(expected, x_mod.retrieve());
97    }
98}
crypto_bigint/uint/modular/constant_mod/const_sub.rs

crypto_bigint/uint/modular/constant_mod/
const_sub.rs
