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use core::ops::{Sub, SubAssign};
use crate::modular::sub::sub_montgomery_form;
use super::DynResidue;
impl<const LIMBS: usize> DynResidue<LIMBS> {
/// Subtracts `rhs`.
pub const fn sub(&self, rhs: &Self) -> Self {
Self {
montgomery_form: sub_montgomery_form(
&self.montgomery_form,
&rhs.montgomery_form,
&self.residue_params.modulus,
),
residue_params: self.residue_params,
}
}
}
impl<const LIMBS: usize> Sub<&DynResidue<LIMBS>> for &DynResidue<LIMBS> {
type Output = DynResidue<LIMBS>;
fn sub(self, rhs: &DynResidue<LIMBS>) -> DynResidue<LIMBS> {
debug_assert_eq!(self.residue_params, rhs.residue_params);
self.sub(rhs)
}
}
impl<const LIMBS: usize> Sub<DynResidue<LIMBS>> for &DynResidue<LIMBS> {
type Output = DynResidue<LIMBS>;
#[allow(clippy::op_ref)]
fn sub(self, rhs: DynResidue<LIMBS>) -> DynResidue<LIMBS> {
self - &rhs
}
}
impl<const LIMBS: usize> Sub<&DynResidue<LIMBS>> for DynResidue<LIMBS> {
type Output = DynResidue<LIMBS>;
#[allow(clippy::op_ref)]
fn sub(self, rhs: &DynResidue<LIMBS>) -> DynResidue<LIMBS> {
&self - rhs
}
}
impl<const LIMBS: usize> Sub<DynResidue<LIMBS>> for DynResidue<LIMBS> {
type Output = DynResidue<LIMBS>;
fn sub(self, rhs: DynResidue<LIMBS>) -> DynResidue<LIMBS> {
&self - &rhs
}
}
impl<const LIMBS: usize> SubAssign<&DynResidue<LIMBS>> for DynResidue<LIMBS> {
fn sub_assign(&mut self, rhs: &DynResidue<LIMBS>) {
*self = *self - rhs;
}
}
impl<const LIMBS: usize> SubAssign<DynResidue<LIMBS>> for DynResidue<LIMBS> {
fn sub_assign(&mut self, rhs: DynResidue<LIMBS>) {
*self -= &rhs;
}
}
#[cfg(test)]
mod tests {
use crate::{
modular::runtime_mod::{DynResidue, DynResidueParams},
U256,
};
#[test]
fn sub_overflow() {
let params = DynResidueParams::new(&U256::from_be_hex(
"ffffffff00000000ffffffffffffffffbce6faada7179e84f3b9cac2fc632551",
));
let x =
U256::from_be_hex("44acf6b7e36c1342c2c5897204fe09504e1e2efb1a900377dbc4e7a6a133ec56");
let mut x_mod = DynResidue::new(&x, params);
let y =
U256::from_be_hex("d5777c45019673125ad240f83094d4252d829516fac8601ed01979ec1ec1a251");
let y_mod = DynResidue::new(&y, params);
x_mod -= &y_mod;
let expected =
U256::from_be_hex("6f357a71e1d5a03167f34879d469352add829491c6df41ddff65387d7ed56f56");
assert_eq!(expected, x_mod.retrieve());
}
}
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