rustfft 4.1.0

Compute FFTs of any size in O(nlogn) time, in pure Rust.
Documentation 
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use num_complex::Complex;
use num_traits::Zero;

use std::sync::Arc;

use rand::distributions::{Distribution, Uniform};
use rand::{rngs::StdRng, SeedableRng};

use crate::algorithm::{butterflies, DFT};
use crate::FFT;

/// The seed for the random number generator used to generate
/// random signals. It's defined here so that we have deterministic
/// tests
const RNG_SEED: [u8; 32] = [
    1, 9, 1, 0, 1, 1, 4, 3, 1, 4, 9, 8, 4, 1, 4, 8, 2, 8, 1, 2, 2, 2, 6, 1, 2, 3, 4, 5, 6, 7, 8, 9,
];

pub fn random_signal(length: usize) -> Vec<Complex<f32>> {
    let mut sig = Vec::with_capacity(length);
    let normal_dist = Uniform::new(0.0, 10.0);
    let mut rng: StdRng = SeedableRng::from_seed(RNG_SEED);
    for _ in 0..length {
        sig.push(Complex {
            re: (normal_dist.sample(&mut rng) as f32),
            im: (normal_dist.sample(&mut rng) as f32),
        });
    }
    return sig;
}

pub fn compare_vectors(vec1: &[Complex<f32>], vec2: &[Complex<f32>]) -> bool {
    assert_eq!(vec1.len(), vec2.len());
    let mut sse = 0f32;
    for (&a, &b) in vec1.iter().zip(vec2.iter()) {
        sse = sse + (a - b).norm();
    }
    return (sse / vec1.len() as f32) < 0.1f32;
}

pub fn check_fft_algorithm(fft: &dyn FFT<f32>, size: usize, inverse: bool) {
    assert_eq!(fft.len(), size, "Algorithm reported incorrect size");
    assert_eq!(
        fft.is_inverse(),
        inverse,
        "Algorithm reported incorrect inverse value"
    );

    let n = 5;

    //test the forward direction
    let dft = DFT::new(size, inverse);

    // set up buffers
    let mut expected_input = random_signal(size * n);
    let mut actual_input = expected_input.clone();
    let mut multi_input = expected_input.clone();

    let mut expected_output = vec![Zero::zero(); size * n];
    let mut actual_output = expected_output.clone();
    let mut multi_output = expected_output.clone();

    // perform the test
    dft.process_multi(&mut expected_input, &mut expected_output);
    fft.process_multi(&mut multi_input, &mut multi_output);

    for (input_chunk, output_chunk) in actual_input
        .chunks_exact_mut(size)
        .zip(actual_output.chunks_exact_mut(size))
    {
        fft.process(input_chunk, output_chunk);
    }

    //assert!(compare_vectors(&expected_output, &actual_output), "process() failed, length = {}, inverse = {}", size, inverse);
    assert!(
        compare_vectors(&expected_output, &multi_output),
        "process_multi() failed, length = {}, inverse = {}",
        size,
        inverse
    );
}

pub fn make_butterfly(len: usize, inverse: bool) -> Arc<dyn butterflies::FFTButterfly<f32>> {
    match len {
        2 => Arc::new(butterflies::Butterfly2::new(inverse)),
        3 => Arc::new(butterflies::Butterfly3::new(inverse)),
        4 => Arc::new(butterflies::Butterfly4::new(inverse)),
        5 => Arc::new(butterflies::Butterfly5::new(inverse)),
        6 => Arc::new(butterflies::Butterfly6::new(inverse)),
        7 => Arc::new(butterflies::Butterfly7::new(inverse)),
        8 => Arc::new(butterflies::Butterfly8::new(inverse)),
        16 => Arc::new(butterflies::Butterfly16::new(inverse)),
        _ => panic!("Invalid butterfly size: {}", len),
    }
}