/*
* Fast discrete cosine transform algorithms (Rust)
*
* Copyright (c) 2019 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;
use fft;
/*
* Computes the unscaled DCT type II on the specified array in place.
* The array length must be a power of 2 or zero.
* For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II .
*/
pub fn transform(vector: &mut [f64]) {
let len: usize = vector.len();
let halflen: usize = len / 2;
let mut real = vec![0.0f64; len];
for i in 0 .. halflen {
real[i] = vector[i * 2];
real[len - 1 - i] = vector[i * 2 + 1];
}
if len % 2 == 1 {
real[halflen] = vector[len - 1];
}
for x in vector.iter_mut() {
*x = 0.0;
}
fft::transform(&mut real, vector);
for i in 0 .. len {
let temp = (i as f64) * std::f64::consts::PI / ((len as f64) * 2.0);
vector[i] = real[i] * temp.cos() + vector[i] * temp.sin();
}
}
/*
* Computes the unscaled DCT type III on the specified array in place.
* The array length must be a power of 2 or zero.
* For the formula, see https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-III .
*/
pub fn inverse_transform(vector: &mut [f64]) {
let len: usize = vector.len();
if len > 0 {
vector[0] /= 2.0;
}
let mut real = vec![0.0f64; len];
for i in 0 .. len {
let temp = (i as f64) * std::f64::consts::PI / ((len as f64) * 2.0);
real[i] = vector[i] * temp.cos();
vector[i] *= -temp.sin();
}
fft::transform(&mut real, vector);
let halflen: usize = len / 2;
for i in 0 .. halflen {
vector[i * 2 + 0] = real[i];
vector[i * 2 + 1] = real[len - 1 - i];
}
if len % 2 == 1 {
vector[len - 1] = real[halflen];
}
}