use alloc::vec::Vec;
use crate::packed::PackedField;
use crate::types::Field;
pub struct ZeroPolyOnCoset<F: Field> {
n: F,
rate: usize,
evals: Vec<F>,
inverses: Vec<F>,
}
impl<F: Field> ZeroPolyOnCoset<F> {
pub fn new(n_log: usize, rate_bits: usize) -> Self {
let g_pow_n = F::coset_shift().exp_power_of_2(n_log);
let evals = F::two_adic_subgroup(rate_bits)
.into_iter()
.map(|x| g_pow_n * x - F::ONE)
.collect::<Vec<_>>();
let inverses = F::batch_multiplicative_inverse(&evals);
Self {
n: F::from_canonical_usize(1 << n_log),
rate: 1 << rate_bits,
evals,
inverses,
}
}
pub fn eval(&self, i: usize) -> F {
self.evals[i % self.rate]
}
pub fn eval_inverse(&self, i: usize) -> F {
self.inverses[i % self.rate]
}
pub fn eval_inverse_packed<P: PackedField<Scalar = F>>(&self, i_start: usize) -> P {
let mut packed = P::ZEROS;
packed
.as_slice_mut()
.iter_mut()
.enumerate()
.for_each(|(j, packed_j)| *packed_j = self.eval_inverse(i_start + j));
packed
}
pub fn eval_l_0(&self, i: usize, x: F) -> F {
self.eval(i) * (self.n * (x - F::ONE)).inverse()
}
}