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    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: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<&ConstMontyForm<MOD, LIMBS>>
22    for &ConstMontyForm<MOD, LIMBS>
23{
24    type Output = ConstMontyForm<MOD, LIMBS>;
25    fn sub(self, rhs: &ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
26        self.sub(rhs)
27    }
28}
29
30impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<ConstMontyForm<MOD, LIMBS>>
31    for &ConstMontyForm<MOD, LIMBS>
32{
33    type Output = ConstMontyForm<MOD, LIMBS>;
34    #[allow(clippy::op_ref)]
35    fn sub(self, rhs: ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
36        self - &rhs
37    }
38}
39
40impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<&ConstMontyForm<MOD, LIMBS>>
41    for ConstMontyForm<MOD, LIMBS>
42{
43    type Output = ConstMontyForm<MOD, LIMBS>;
44    #[allow(clippy::op_ref)]
45    fn sub(self, rhs: &ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
46        &self - rhs
47    }
48}
49
50impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> Sub<ConstMontyForm<MOD, LIMBS>>
51    for ConstMontyForm<MOD, LIMBS>
52{
53    type Output = ConstMontyForm<MOD, LIMBS>;
54    fn sub(self, rhs: ConstMontyForm<MOD, LIMBS>) -> ConstMontyForm<MOD, LIMBS> {
55        &self - &rhs
56    }
57}
58
59impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> SubAssign<&Self>
60    for ConstMontyForm<MOD, LIMBS>
61{
62    fn sub_assign(&mut self, rhs: &Self) {
63        *self = *self - rhs;
64    }
65}
66
67impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> SubAssign<Self>
68    for ConstMontyForm<MOD, LIMBS>
69{
70    fn sub_assign(&mut self, rhs: Self) {
71        *self -= &rhs;
72    }
73}
74
75#[cfg(test)]
76mod tests {
77    use crate::{
78        const_monty_form, impl_modulus, modular::const_monty_form::ConstMontyParams, U256,
79    };
80
81    impl_modulus!(
82        Modulus,
83        U256,
84        "ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551"
85    );
86
87    #[test]
88    fn sub_overflow() {
89        let x =
90            U256::from_be_hex("44acf6b7e36c1342c2c5897204fe09504e1e2efb1a900377dbc4e7a6a133ec56");
91        let mut x_mod = const_monty_form!(x, Modulus);
92
93        let y =
94            U256::from_be_hex("d5777c45019673125ad240f83094d4252d829516fac8601ed01979ec1ec1a251");
95        let y_mod = const_monty_form!(y, Modulus);
96
97        x_mod -= &y_mod;
98
99        let expected =
100            U256::from_be_hex("6f357a71e1d5a03167f34879d469352add829491c6df41ddff65387d7ed56f56");
101
102        assert_eq!(expected, x_mod.retrieve());
103    }
104}
crypto_bigint/modular/const_monty_form/sub.rs

crypto_bigint/modular/const_monty_form/
sub.rs
