Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

chore: add a FFT trait to deduplicate FFT code #291

Merged
merged 1 commit into from
Sep 26, 2024
Merged

chore: add a FFT trait to deduplicate FFT code #291

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
72 changes: 22 additions & 50 deletions cryptography/polynomial/src/domain.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -223,60 +223,27 @@ impl Domain {
}
}

/// Computes a FFT of the field elements(scalars).
///
/// Note: This is essentially multiple inner products.
///
/// TODO: This method is still duplicated below
fn fft_scalar_inplace(twiddle_factors: &[Scalar], a: &mut [Scalar]) {
let n = a.len();
let log_n = log2_pow2(n);
assert_eq!(n, 1 << log_n);

// Bit-reversal permutation
for k in 0..n {
let rk = bitreverse(k as u32, log_n) as usize;
if k < rk {
a.swap(rk, k);
}
}

let mut m = 1;
for s in 0..log_n {
let w_m = twiddle_factors[s as usize];
for k in (0..n).step_by(2 * m) {
let mut w = Scalar::ONE;

for j in 0..m {
let t = if w == Scalar::ONE {
a[k + j + m]
} else if w == -Scalar::ONE {
-a[k + j + m]
} else {
a[k + j + m] * w
};
use std::ops::{Add, Mul, Neg, Sub};

trait FFTElement:
Sized
+ Copy
+ Add<Output = Self>
+ Sub<Output = Self>
+ Mul<Scalar, Output = Self>
+ Neg<Output = Self>
{
}

let u = a[k + j];
impl FFTElement for Scalar {}

a[k + j] = u + t;
a[k + j + m] = u - t;

w *= w_m;
}
}
m *= 2;
}
}
impl FFTElement for G1Projective {}

/// Computes a FFT of the group elements(points).
///
/// Note: This is essentially multiple multi-scalar multiplications.
fn fft_g1_inplace(twiddle_factors: &[Scalar], a: &mut [G1Projective]) {
fn fft_inplace<T: FFTElement>(twiddle_factors: &[Scalar], a: &mut [T]) {
let n = a.len();
let log_n = log2_pow2(n);
assert_eq!(n, 1 << log_n);

// Bit-reversal permutation
for k in 0..n {
let rk = bitreverse(k as u32, log_n) as usize;
if k < rk {
Expand All @@ -294,12 +261,9 @@ fn fft_g1_inplace(twiddle_factors: &[Scalar], a: &mut [G1Projective]) {
a[k + j + m]
} else if w == -Scalar::ONE {
-a[k + j + m]
} else if a[k + j + m].is_identity().into() {
G1Projective::identity()
kevaundray marked this conversation as resolved.
Show resolved Hide resolved
} else {
a[k + j + m] * w
};

let u = a[k + j];
a[k + j] = u + t;
a[k + j + m] = u - t;
Expand All @@ -310,6 +274,14 @@ fn fft_g1_inplace(twiddle_factors: &[Scalar], a: &mut [G1Projective]) {
}
}

fn fft_scalar_inplace(twiddle_factors: &[Scalar], a: &mut [Scalar]) {
fft_inplace(twiddle_factors, a);
}

fn fft_g1_inplace(twiddle_factors: &[Scalar], a: &mut [G1Projective]) {
fft_inplace(twiddle_factors, a);
}

fn bitreverse(mut n: u32, l: u32) -> u32 {
let mut r = 0;
for _ in 0..l {
Expand Down
Loading