/* * Fast discrete cosine transform algorithms (C) * * Copyright (c) 2021 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. */ #include #include #include #include "fast-dct-fft.h" #include "fft-real-pair.h" // DCT type II, unscaled bool FastDctFft_transform(double vector[], size_t len) { // Allocate memory if (SIZE_MAX / sizeof(double) < len) return false; double *real = malloc(len * sizeof(double)); if (real == NULL) return false; // Preprocess the vectors size_t halfLen = len / 2; for (size_t i = 0; i < halfLen; i++) { real[i] = vector[i * 2]; real[len - 1 - i] = vector[i * 2 + 1]; } if (len % 2 == 1) real[halfLen] = vector[len - 1]; for (size_t i = 0; i < len; i++) vector[i] = 0; // Transform and postprocess if (!Fft_transform(real, vector, len)) { free(real); return false; } for (size_t i = 0; i < len; i++) { double temp = i * M_PI / (len * 2); vector[i] = real[i] * cos(temp) + vector[i] * sin(temp); } free(real); return true; } // DCT type III, unscaled bool FastDctFft_inverseTransform(double vector[], size_t len) { // Allocate memory if (SIZE_MAX / sizeof(double) < len) return false; double *real = malloc(len * sizeof(double)); if (real == NULL) return false; // Preprocess and transform if (len > 0) vector[0] /= 2; for (size_t i = 0; i < len; i++) { double temp = i * M_PI / (len * 2); real[i] = vector[i] * cos(temp); vector[i] *= -sin(temp); } if (!Fft_transform(real, vector, len)) { free(real); return false; } // Postprocess the vectors size_t halfLen = len / 2; for (size_t i = 0; i < halfLen; i++) { vector[i * 2 + 0] = real[i]; vector[i * 2 + 1] = real[len - 1 - i]; } if (len % 2 == 1) vector[len - 1] = real[halfLen]; free(real); return true; }