logos-storage/plonky2
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This commit is contained in:
Daniel Lubarov 2021-05-13 15:44:36 -07:00
parent 6d03dd06f5
commit 7f445686ee
2 changed files with 37 additions and 37 deletions
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42
src/polynomial/division.rs
View File

@ -1,16 +1,16 @@
use crate::field::fft::{fft, ifft};
use crate::field::field::Field;
use crate::polynomial::polynomial::PolynomialCoeffs;
use crate::util::log2_strict;
use crate::util::{log2_strict, log2_ceil};
impl<F: Field> PolynomialCoeffs<F> {
/// Polynomial division.
/// Returns `(q, r)`, the quotient and remainder of the polynomial division of `a` by `b`.
pub(crate) fn div_rem(&self, b: &Self) -> (Self, Self) {
let (a_degree_plug_1, b_degree_plus_1) = (self.degree_plus_one(), b.degree_plus_one());
if self.is_zero() {
if a_degree_plug_1 == 0 {
(Self::zero(1), Self::empty())
} else if b.is_zero() {
} else if b_degree_plus_1 == 0 {
panic!("Division by zero polynomial");
} else if a_degree_plug_1 < b_degree_plus_1 {
(Self::zero(1), self.clone())
@ -41,9 +41,9 @@ impl<F: Field> PolynomialCoeffs<F> {
let b = b.trimmed();
let (a_degree_plus_1, b_degree_plus_1) = (self.degree_plus_one(), b.degree_plus_one());
if self.is_zero() {
if a_degree_plus_1 == 0 {
(Self::zero(1), Self::empty())
} else if b.is_zero() {
} else if b_degree_plus_1 == 0 {
panic!("Division by zero polynomial");
} else if a_degree_plus_1 < b_degree_plus_1 {
(Self::zero(1), self.clone())
@ -124,6 +124,38 @@ impl<F: Field> PolynomialCoeffs<F> {
});
p
}
/// Computes the inverse of `self` modulo `x^n`.
pub(crate) fn inv_mod_xn(&self, n: usize) -> Self {
assert!(self.coeffs[0].is_nonzero(), "Inverse doesn't exist.");
let mut h = self.padded(n);
let mut a = Self::empty();
a.coeffs.push(h.coeffs[0].inverse());
for i in 0..log2_ceil(n) {
let l = 1 << i;
let h0 = h.coeffs[..l].to_vec().into();
let mut h1: Self = h.coeffs[l..].to_vec().into();
let mut c = &a * &h0;
if l == c.len() {
c = Self::zero(1);
} else {
c.coeffs.drain(0..l);
}
h1.trim();
let mut tmp = &a * &h1;
tmp = &tmp + &c;
tmp.coeffs.iter_mut().for_each(|x| *x = -(*x));
tmp.trim();
let mut b = &a * &tmp;
b.trim();
if b.len() > l {
b.coeffs.drain(l..);
}
a.coeffs.extend_from_slice(&b.coeffs);
}
a.coeffs.drain(n..);
a
}
}
#[cfg(test)]

32
src/polynomial/polynomial.rs
View File

@ -149,38 +149,6 @@ impl<F: Field> PolynomialCoeffs<F> {
.map_or(F::ZERO, |x| *x)
}
/// Computes the inverse of `self` modulo `x^n`.
pub(crate) fn inv_mod_xn(&self, n: usize) -> Self {
assert!(self.coeffs[0].is_nonzero(), "Inverse doesn't exist.");
let mut h = self.padded(n);
let mut a = Self::empty();
a.coeffs.push(h.coeffs[0].inverse());
for i in 0..log2_ceil(n) {
let l = 1 << i;
let h0 = h.coeffs[..l].to_vec().into();
let mut h1: Self = h.coeffs[l..].to_vec().into();
let mut c = &a * &h0;
if l == c.len() {
c = Self::zero(1);
} else {
c.coeffs.drain(0..l);
}
h1.trim();
let mut tmp = a.mul(&h1);
tmp = tmp.add(&c);
tmp.coeffs.iter_mut().for_each(|x| *x = -(*x));
tmp.trim();
let mut b = &a * &tmp;
b.trim();
if b.len() > l {
b.coeffs.drain(l..);
}
a.coeffs.extend_from_slice(&b.coeffs);
}
a.coeffs.drain(n..);
a
}
/// Reverse the order of the coefficients, not taking into account the leading zero coefficients.
pub(crate) fn rev(&self) -> Self {
Self::new(self.trimmed().coeffs.into_iter().rev().collect())