/* * 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]; } }