/* * 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 }