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use crate::*;
#[derive(Clone, Debug)]
pub struct QuotientRing<A>
where
A: EuclideanDomain,
{
base: A,
modulo: A::Elem,
}
impl<A> QuotientRing<A>
where
A: EuclideanDomain,
{
pub fn new(base: A, modulo: A::Elem) -> Self {
assert!(base.contains(&modulo));
QuotientRing { base, modulo }
}
pub fn base(&self) -> &A {
&self.base
}
pub fn modulo(&self) -> &A::Elem {
&self.modulo
}
}
impl<A> Domain for QuotientRing<A>
where
A: EuclideanDomain,
{
type Elem = A::Elem;
fn contains(&self, elem: &Self::Elem) -> bool {
self.base.reduced(elem, &self.modulo)
}
fn equals(&self, elem1: &Self::Elem, elem2: &Self::Elem) -> bool {
self.base.equals(elem1, elem2)
}
}
impl<A> Semigroup for QuotientRing<A>
where
A: EuclideanDomain,
{
fn mul(&self, elem1: &Self::Elem, elem2: &Self::Elem) -> Self::Elem {
self.base.rem(&self.base.mul(elem1, elem2), &self.modulo)
}
}
impl<A> Monoid for QuotientRing<A>
where
A: EuclideanDomain,
{
fn one(&self) -> Self::Elem {
self.base.one()
}
fn is_one(&self, elem: &Self::Elem) -> bool {
self.base.is_one(elem)
}
fn try_inv(&self, elem: &Self::Elem) -> Option<Self::Elem> {
let (g, _, r) = self.base.extended_gcd(&self.modulo, elem);
self.base.try_inv(&g).map(|a| self.mul(&a, &r))
}
}
impl<A> AbelianGroup for QuotientRing<A>
where
A: EuclideanDomain,
{
fn zero(&self) -> Self::Elem {
self.base.zero()
}
fn neg(&self, elem: &Self::Elem) -> Self::Elem {
self.base.rem(&self.base.neg(elem), &self.modulo)
}
fn add(&self, elem1: &Self::Elem, elem2: &Self::Elem) -> Self::Elem {
self.base.rem(&self.base.add(elem1, elem2), &self.modulo)
}
}
impl<A> UnitaryRing for QuotientRing<A> where A: EuclideanDomain {}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn zstar_1584() {
let ring = QuotientRing::new(I32, 1584);
let mut count = 0;
for a in 0..1584 {
assert!(ring.contains(&a));
if a != 0 {
if let Some(b) = ring.try_inv(&a) {
assert!(ring.contains(&b));
assert!(ring.is_one(&ring.mul(&a, &b)));
count += 1;
}
}
}
assert_eq!(count, 8 * 6 * 10);
}
}