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use std::fmt::Debug;
use std::marker::PhantomData;
use halo2_base::{utils::modulus, AssignedValue, Context};
use num_bigint::BigUint;
use crate::impl_field_ext_chip_common;
use super::{
vector::{FieldVector, FieldVectorChip},
FieldChip, FieldExtConstructor, PrimeField, PrimeFieldChip,
};
#[derive(Clone, Copy, Debug)]
pub struct Fp2Chip<'a, F: PrimeField, FpChip: FieldChip<F>, Fp2>(
pub FieldVectorChip<'a, F, FpChip>,
PhantomData<Fp2>,
);
impl<'a, F: PrimeField, FpChip: PrimeFieldChip<F>, Fp2: ff::Field> Fp2Chip<'a, F, FpChip, Fp2>
where
FpChip::FieldType: PrimeField,
{
pub fn new(fp_chip: &'a FpChip) -> Self {
assert_eq!(
modulus::<FpChip::FieldType>() % 4usize,
BigUint::from(3u64),
"p must be 3 (mod 4) for the polynomial u^2 + 1 to be irreducible"
);
Self(FieldVectorChip::new(fp_chip), PhantomData)
}
pub fn fp_chip(&self) -> &FpChip {
self.0.fp_chip
}
pub fn conjugate(
&self,
ctx: &mut Context<F>,
a: FieldVector<FpChip::FieldPoint>,
) -> FieldVector<FpChip::FieldPoint> {
let mut a = a.0;
assert_eq!(a.len(), 2);
let neg_a1 = self.fp_chip().negate(ctx, a.pop().unwrap());
FieldVector(vec![a.pop().unwrap(), neg_a1])
}
pub fn neg_conjugate(
&self,
ctx: &mut Context<F>,
a: FieldVector<FpChip::FieldPoint>,
) -> FieldVector<FpChip::FieldPoint> {
assert_eq!(a.0.len(), 2);
let mut a = a.0.into_iter();
let neg_a0 = self.fp_chip().negate(ctx, a.next().unwrap());
FieldVector(vec![neg_a0, a.next().unwrap()])
}
}
impl<'a, F, FpChip, Fp2> FieldChip<F> for Fp2Chip<'a, F, FpChip, Fp2>
where
F: PrimeField,
FpChip::FieldType: PrimeField,
FpChip: PrimeFieldChip<F>,
Fp2: ff::Field + FieldExtConstructor<FpChip::FieldType, 2>,
FieldVector<FpChip::UnsafeFieldPoint>: From<FieldVector<FpChip::FieldPoint>>,
FieldVector<FpChip::FieldPoint>: From<FieldVector<FpChip::ReducedFieldPoint>>,
{
const PRIME_FIELD_NUM_BITS: u32 = FpChip::FieldType::NUM_BITS;
type UnsafeFieldPoint = FieldVector<FpChip::UnsafeFieldPoint>;
type FieldPoint = FieldVector<FpChip::FieldPoint>;
type ReducedFieldPoint = FieldVector<FpChip::ReducedFieldPoint>;
type FieldType = Fp2;
type RangeChip = FpChip::RangeChip;
fn get_assigned_value(&self, x: &Self::UnsafeFieldPoint) -> Fp2 {
assert_eq!(x.0.len(), 2);
let c0 = self.fp_chip().get_assigned_value(&x[0]);
let c1 = self.fp_chip().get_assigned_value(&x[1]);
Fp2::new([c0, c1])
}
fn mul_no_carry(
&self,
ctx: &mut Context<F>,
a: impl Into<Self::UnsafeFieldPoint>,
b: impl Into<Self::UnsafeFieldPoint>,
) -> Self::UnsafeFieldPoint {
let a = a.into().0;
let b = b.into().0;
assert_eq!(a.len(), 2);
assert_eq!(b.len(), 2);
let fp_chip = self.fp_chip();
let mut ab_coeffs = Vec::with_capacity(4);
for a_i in a {
for b_j in b.iter() {
let coeff = fp_chip.mul_no_carry(ctx, &a_i, b_j);
ab_coeffs.push(coeff);
}
}
let a0b0_minus_a1b1 = fp_chip.sub_no_carry(ctx, &ab_coeffs[0], &ab_coeffs[3]);
let a0b1_plus_a1b0 = fp_chip.add_no_carry(ctx, &ab_coeffs[1], &ab_coeffs[2]);
FieldVector(vec![a0b0_minus_a1b1, a0b1_plus_a1b0])
}
impl_field_ext_chip_common!();
}
mod bn254 {
use crate::fields::FieldExtConstructor;
use crate::halo2_proofs::halo2curves::bn256::{Fq, Fq2};
impl FieldExtConstructor<Fq, 2> for Fq2 {
fn new(c: [Fq; 2]) -> Self {
Fq2 { c0: c[0], c1: c[1] }
}
fn coeffs(&self) -> Vec<Fq> {
vec![self.c0, self.c1]
}
}
}