/* * Fast discrete cosine transform algorithms (C) * * Copyright (c) 2017 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 "naive-dct.h" // DCT type II, unscaled. // See: https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II double *NaiveDct_transform(double vector[], size_t len) { if (SIZE_MAX / sizeof(double) < len) return NULL; double *result = malloc(len * sizeof(double)); if (result == NULL) return NULL; double factor = M_PI / len; for (size_t i = 0; i < len; i++) { double sum = 0; for (size_t j = 0; j < len; j++) sum += vector[j] * cos((j + 0.5) * i * factor); result[i] = sum; } return result; } // DCT type III, unscaled. // See: https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-III double *NaiveDct_inverseTransform(double vector[], size_t len) { if (SIZE_MAX / sizeof(double) < len) return NULL; double *result = malloc(len * sizeof(double)); if (result == NULL) return NULL; double factor = M_PI / len; for (size_t i = 0; i < len; i++) { double sum = vector[0] / 2; for (size_t j = 1; j < len; j++) sum += vector[j] * cos(j * (i + 0.5) * factor); result[i] = sum; } return result; }