use core::ops::{Sub, SubAssign};
use crate::modular::sub::sub_montgomery_form;
use super::{Residue, ResidueParams};
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Residue<MOD, LIMBS> {
pub const fn sub(&self, rhs: &Self) -> Self {
Self {
montgomery_form: sub_montgomery_form(
&self.montgomery_form,
&rhs.montgomery_form,
&MOD::MODULUS,
),
phantom: core::marker::PhantomData,
}
}
}
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<&Residue<MOD, LIMBS>>
for &Residue<MOD, LIMBS>
{
type Output = Residue<MOD, LIMBS>;
fn sub(self, rhs: &Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
self.sub(rhs)
}
}
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<Residue<MOD, LIMBS>>
for &Residue<MOD, LIMBS>
{
type Output = Residue<MOD, LIMBS>;
#[allow(clippy::op_ref)]
fn sub(self, rhs: Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
self - &rhs
}
}
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<&Residue<MOD, LIMBS>>
for Residue<MOD, LIMBS>
{
type Output = Residue<MOD, LIMBS>;
#[allow(clippy::op_ref)]
fn sub(self, rhs: &Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
&self - rhs
}
}
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> Sub<Residue<MOD, LIMBS>>
for Residue<MOD, LIMBS>
{
type Output = Residue<MOD, LIMBS>;
fn sub(self, rhs: Residue<MOD, LIMBS>) -> Residue<MOD, LIMBS> {
&self - &rhs
}
}
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> SubAssign<&Self> for Residue<MOD, LIMBS> {
fn sub_assign(&mut self, rhs: &Self) {
*self = *self - rhs;
}
}
impl<MOD: ResidueParams<LIMBS>, const LIMBS: usize> SubAssign<Self> for Residue<MOD, LIMBS> {
fn sub_assign(&mut self, rhs: Self) {
*self -= &rhs;
}
}
#[cfg(test)]
mod tests {
use crate::{const_residue, impl_modulus, modular::constant_mod::ResidueParams, U256};
impl_modulus!(
Modulus,
U256,
"ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551"
);
#[test]
fn sub_overflow() {
let x =
U256::from_be_hex("44acf6b7e36c1342c2c5897204fe09504e1e2efb1a900377dbc4e7a6a133ec56");
let mut x_mod = const_residue!(x, Modulus);
let y =
U256::from_be_hex("d5777c45019673125ad240f83094d4252d829516fac8601ed01979ec1ec1a251");
let y_mod = const_residue!(y, Modulus);
x_mod -= &y_mod;
let expected =
U256::from_be_hex("6f357a71e1d5a03167f34879d469352add829491c6df41ddff65387d7ed56f56");
assert_eq!(expected, x_mod.retrieve());
}
}