pounder_test/dsp/build.rs

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Rust
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use std::env;
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use std::f64::consts::PI;
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use std::fs::File;
use std::io::prelude::*;
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use std::path::Path;
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fn write_cossin_table() {
const DEPTH: usize = 7;
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let out_dir = env::var_os("OUT_DIR").unwrap();
let dest_path = Path::new(&out_dir).join("cossin_table.rs");
let mut file = File::create(dest_path).unwrap();
writeln!(file, "pub(crate) const COSSIN_DEPTH: usize = {};", DEPTH)
.unwrap();
write!(
file,
"pub(crate) const COSSIN: [u32; 1 << COSSIN_DEPTH] = ["
)
.unwrap();
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// Treat sin and cos as unsigned values since the sign will always be
// positive in the range [0, pi/4).
// No headroom for interpolation rounding error (this is needed for
// DEPTH = 6 for example).
const AMPLITUDE: f64 = u16::MAX as f64;
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for i in 0..(1 << DEPTH) {
if i % 4 == 0 {
write!(file, "\n ").unwrap();
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}
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// Use midpoint samples to save one entry in the LUT
let (sin, cos) =
(PI / 4. * ((i as f64 + 0.5) / (1 << DEPTH) as f64)).sin_cos();
// Add one bit accuracy to cos due to 0.5 < cos(z) <= 1 for |z| < pi/4
// The -1 LSB is cancelled when unscaling with the biased half amplitude
let cos = ((cos * 2. - 1.) * AMPLITUDE - 1.).round() as u32;
let sin = (sin * AMPLITUDE).round() as u32;
write!(file, " {},", cos + (sin << 16)).unwrap();
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}
writeln!(file, "\n];").unwrap();
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println!("cargo:rerun-if-changed=build.rs");
}
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fn main() {
write_cossin_table();
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}