embfft 0.2.1

Non-blocking FFT for embedded systems
Documentation 
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/* embfft | build.rs
 * Copyright (c) 2025 L. Sartory
 * SPDX-License-Identifier: MIT
 */

/******************************************************************************/

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::Path;

/******************************************************************************/

fn compute_theta_table() -> [f64; 64] {
    (0..64)
        .map(|i| f64::atan2(1.0, f64::powf(2.0, i as _)))
        .collect::<Vec<f64>>()
        .try_into()
        .unwrap()
}

fn compute_k_table() -> [f64; 64] {
    let mut k = 1.0;
    (0..64)
        .map(|i| {
            k *= 1.0 / f64::sqrt(1.0 + f64::powf(2.0, -2.0 * i as f64));
            k
        })
        .collect::<Vec<f64>>()
        .try_into()
        .unwrap()
}

/******************************************************************************/

fn main() {
    let out_dir = env::var_os("OUT_DIR").unwrap();
    let dest_path = Path::new(&out_dir).join("cordic_tables.rs");
    let mut f = File::create(dest_path).unwrap();

    let theta_table = compute_theta_table();
    writeln!(&mut f, "#[allow(clippy::approx_constant)]").unwrap();
    writeln!(
        &mut f,
        "const THETA_TABLE: [f64; {}] = {:?};",
        theta_table.len(),
        theta_table
    )
    .unwrap();
    let k_table = compute_k_table();
    writeln!(
        &mut f,
        "const K_TABLE: [f64; {}] = {:?};",
        k_table.len(),
        k_table
    )
    .unwrap();
}