/*
* Fast discrete cosine transform algorithms (Rust)
*
* Copyright (c) 2024 Project Nayuki. (MIT License)
* https://www.nayuki.io/page/fast-discrete-cosine-transform-algorithms
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
* - The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* - The Software is provided "as is", without warranty of any kind, express or
* implied, including but not limited to the warranties of merchantability,
* fitness for a particular purpose and noninfringement. In no event shall the
* authors or copyright holders be liable for any claim, damages or other
* liability, whether in an action of contract, tort or otherwise, arising from,
* out of or in connection with the Software or the use or other dealings in the
* Software.
*/
use std;
/*
* Computes the unscaled DCT type II on the specified array, returning a new array.
* The array length can be any value, starting from zero. The returned array has the same length.
* For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II .
*/
pub fn transform(vector: &[f64]) -> Vec {
let mut result = Vec::::with_capacity(vector.len());
let factor: f64 = std::f64::consts::PI / (vector.len() as f64);
for i in 0 .. vector.len() {
let mut sum = 0.0f64;
for j in 0 .. vector.len() {
sum += vector[j] * (((j as f64) + 0.5) * (i as f64) * factor).cos();
}
result.push(sum);
}
result
}
/*
* Computes the unscaled DCT type III on the specified array, returning a new array.
* The array length can be any value, starting from zero. The returned array has the same length.
* For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-III .
*/
pub fn inverse_transform(vector: &[f64]) -> Vec {
let mut result = Vec::::with_capacity(vector.len());
let factor: f64 = std::f64::consts::PI / (vector.len() as f64);
for i in 0 .. vector.len() {
let mut sum: f64 = vector[0] / 2.0;
for j in 1 .. vector.len() {
sum += vector[j] * ((j as f64) * ((i as f64) + 0.5) * factor).cos();
}
result.push(sum);
}
result
}