crypto_bigint/modular/const_monty_form/
sub.rs

1//! Subtractions between integers in Montgomery form with a constant modulus.
2
3use super::{ConstMontyForm, ConstMontyParams};
4use crate::modular::sub::sub_montgomery_form;
5use core::ops::{Sub, SubAssign};
6
7impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> ConstMontyForm<MOD, LIMBS> {
8    /// Subtracts `rhs`.
9    #[must_use]
10    pub const fn sub(&self, rhs: &Self) -> Self {
11        Self {
12            montgomery_form: sub_montgomery_form(
13                &self.montgomery_form,
14                &rhs.montgomery_form,
15                &MOD::PARAMS.modulus,
16            ),
17            phantom: core::marker::PhantomData,
18        }
19    }
20}
21
22impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<&ConstMontyForm<MOD, LIMBS>>
23    for &ConstMontyForm<MOD, LIMBS>
24{
25    type Output = ConstMontyForm<MOD, LIMBS>;
26    fn sub(self, rhs: &ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
27        self.sub(rhs)
28    }
29}
30
31impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<ConstMontyForm<MOD, LIMBS>>
32    for &ConstMontyForm<MOD, LIMBS>
33{
34    type Output = ConstMontyForm<MOD, LIMBS>;
35    #[allow(clippy::op_ref)]
36    fn sub(self, rhs: ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
37        self - &rhs
38    }
39}
40
41impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<&ConstMontyForm<MOD, LIMBS>>
42    for ConstMontyForm<MOD, LIMBS>
43{
44    type Output = ConstMontyForm<MOD, LIMBS>;
45    #[allow(clippy::op_ref)]
46    fn sub(self, rhs: &ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
47        &self - rhs
48    }
49}
50
51impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<ConstMontyForm<MOD, LIMBS>>
52    for ConstMontyForm<MOD, LIMBS>
53{
54    type Output = ConstMontyForm<MOD, LIMBS>;
55    fn sub(self, rhs: ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
56        &self - &rhs
57    }
58}
59
60impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> SubAssign<&Self>
61    for ConstMontyForm<MOD, LIMBS>
62{
63    fn sub_assign(&mut self, rhs: &Self) {
64        *self = *self - rhs;
65    }
66}
67
68impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> SubAssign<Self>
69    for ConstMontyForm<MOD, LIMBS>
70{
71    fn sub_assign(&mut self, rhs: Self) {
72        *self -= &rhs;
73    }
74}
75
76#[cfg(test)]
77mod tests {
78    use crate::{
79        U256, const_monty_form, const_monty_params, modular::const_monty_form::ConstMontyParams,
80    };
81
82    const_monty_params!(
83        Modulus,
84        U256,
85        "ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551"
86    );
87
88    const_monty_form!(Fe, Modulus);
89
90    #[test]
91    fn sub_overflow() {
92        let x =
93            U256::from_be_hex("44acf6b7e36c1342c2c5897204fe09504e1e2efb1a900377dbc4e7a6a133ec56");
94        let mut x_mod = Fe::new(&x);
95
96        let y =
97            U256::from_be_hex("d5777c45019673125ad240f83094d4252d829516fac8601ed01979ec1ec1a251");
98        let y_mod = Fe::new(&y);
99
100        x_mod -= &y_mod;
101
102        let expected =
103            U256::from_be_hex("6f357a71e1d5a03167f34879d469352add829491c6df41ddff65387d7ed56f56");
104
105        assert_eq!(expected, x_mod.retrieve());
106    }
107}
crypto_bigint/modular/const_monty_form/sub.rs

crypto_bigint/modular/const_monty_form/
sub.rs
