42 lines
1.3 KiB
Rust
42 lines
1.3 KiB
Rust
use std::f64::consts::PI;
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use std::fs::File;
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use std::io::prelude::*;
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use std::path::Path;
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fn write_cossin_table() {
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const DEPTH: usize = 7;
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let mut file =
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File::create(Path::new("src").join("cossin_table.rs")).unwrap();
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writeln!(file, "pub(crate) const COSSIN_DEPTH: usize = {};", DEPTH)
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.unwrap();
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write!(
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file,
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"pub(crate) const COSSIN: [(u16, u16); 1 << COSSIN_DEPTH] = ["
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)
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.unwrap();
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// Treat sin and cos as unsigned values since the sign will always be
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// positive in the range [0, pi/4).
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// No headroom for interpolation rounding error (this is needed for
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// DEPTH = 6 for example).
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const AMPLITUDE: f64 = u16::MAX as f64;
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for i in 0..(1 << DEPTH) {
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// use midpoint samples to save one entry in the LUT
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let phase = (PI / 4. / (1 << DEPTH) as f64) * (i as f64 + 0.5);
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// add one bit accuracy to cos due to 0.5 < cos(z) <= 1 for |z| < pi/4
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let cos = ((phase.cos() - 0.5) * 2. * AMPLITUDE).round() as u16;
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let sin = (phase.sin() * AMPLITUDE).round() as u16;
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if i % 4 == 0 {
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write!(file, "\n ").unwrap();
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}
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write!(file, " ({}, {}),", cos, sin).unwrap();
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}
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writeln!(file, "\n];").unwrap();
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}
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fn main() {
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write_cossin_table();
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}
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