use std::env; use std::f64::consts::PI; use std::fs::File; use std::io::prelude::*; use std::path::Path; fn write_cossin_table() { const DEPTH: usize = 7; 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: [(u16, u16); 1 << COSSIN_DEPTH] = [" ) .unwrap(); // 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; for i in 0..(1 << DEPTH) { // use midpoint samples to save one entry in the LUT let phase = (PI / 4. / (1 << DEPTH) as f64) * (i as f64 + 0.5); // add one bit accuracy to cos due to 0.5 < cos(z) <= 1 for |z| < pi/4 let cos = ((phase.cos() - 0.5) * 2. * AMPLITUDE).round() as u16; let sin = (phase.sin() * AMPLITUDE).round() as u16; if i % 4 == 0 { write!(file, "\n ").unwrap(); } write!(file, " ({}, {}),", cos, sin).unwrap(); } writeln!(file, "\n];").unwrap(); println!("cargo:rerun-if-changed=build.rs"); } fn main() { write_cossin_table(); }