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| 1 | +/* | |
| 2 | + * reference discrete cosine transform (double precision) | |
| 3 | + * Copyright (C) 2009 Dylan Yudaken | |
| 4 | + * | |
| 5 | + * This file is part of FFmpeg. | |
| 6 | + * | |
| 7 | + * FFmpeg is free software; you can redistribute it and/or | |
| 8 | + * modify it under the terms of the GNU Lesser General Public | |
| 9 | + * License as published by the Free Software Foundation; either | |
| 10 | + * version 2.1 of the License, or (at your option) any later version. | |
| 11 | + * | |
| 12 | + * FFmpeg is distributed in the hope that it will be useful, | |
| 13 | + * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 14 | + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 15 | + * Lesser General Public License for more details. | |
| 16 | + * | |
| 17 | + * You should have received a copy of the GNU Lesser General Public | |
| 18 | + * License along with FFmpeg; if not, write to the Free Software | |
| 19 | + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
| 20 | + */ | |
| 21 | + | |
| 22 | +/** | |
| 23 | + * @file libavcodec/dctref.c | |
| 24 | + * reference discrete cosine transform (double precision) | |
| 25 | + * | |
| 26 | + * @author Dylan Yudaken (dyudaken at gmail) | |
| 27 | + * | |
| 28 | + * @note This file could be optimized a lot, but is for | |
| 29 | + * reference and so readability is better. | |
| 30 | + */ | |
| 31 | + | |
| 32 | +#include "libavutil/mathematics.h" | |
| 33 | +static double coefficients[8 * 8]; | |
| 34 | + | |
| 35 | +/** | |
| 36 | + * Initialize the double precision discrete cosine transform | |
| 37 | + * functions fdct & idct. | |
| 38 | + */ | |
| 39 | +av_cold void ff_ref_dct_init(void) | |
| 40 | +{ | |
| 41 | + unsigned int i, j; | |
| 42 | + | |
| 43 | + for (j = 0; j < 8; ++j) { | |
| 44 | + coefficients[j] = sqrt(0.125); | |
| 45 | + for (i = 8; i < 64; i += 8) { | |
| 46 | + coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0); | |
| 47 | + } | |
| 48 | + } | |
| 49 | +} | |
| 50 | + | |
| 51 | +/** | |
| 52 | + * Transform 8x8 block of data with a double precision forward DCT <br> | |
| 53 | + * This is a reference implementation. | |
| 54 | + * | |
| 55 | + * @param block pointer to 8x8 block of data to transform | |
| 56 | + */ | |
| 57 | +void ff_ref_fdct(short *block) | |
| 58 | +{ | |
| 59 | + /* implement the equation: block = coefficients * block * coefficients' */ | |
| 60 | + | |
| 61 | + unsigned int i, j, k; | |
| 62 | + double out[8 * 8]; | |
| 63 | + | |
| 64 | + /* out = coefficients * block */ | |
| 65 | + for (i = 0; i < 64; i += 8) { | |
| 66 | + for (j = 0; j < 8; ++j) { | |
| 67 | + double tmp = 0; | |
| 68 | + for (k = 0; k < 8; ++k) { | |
| 69 | + tmp += coefficients[i + k] * block[k * 8 + j]; | |
| 70 | + } | |
| 71 | + out[i + j] = tmp * 8; | |
| 72 | + } | |
| 73 | + } | |
| 74 | + | |
| 75 | + /* block = out * (coefficients') */ | |
| 76 | + for (j = 0; j < 8; ++j) { | |
| 77 | + for (i = 0; i < 64; i += 8) { | |
| 78 | + double tmp = 0; | |
| 79 | + for (k = 0; k < 8; ++k) { | |
| 80 | + tmp += out[i + k] * coefficients[j * 8 + k]; | |
| 81 | + } | |
| 82 | + block[i + j] = floor(tmp + 0.499999999999); | |
| 83 | + } | |
| 84 | + } | |
| 85 | +} | |
| 86 | + | |
| 87 | +/** | |
| 88 | + * Transform 8x8 block of data with a double precision inverse DCT <br> | |
| 89 | + * This is a reference implementation. | |
| 90 | + * | |
| 91 | + * @param block pointer to 8x8 block of data to transform | |
| 92 | + */ | |
| 93 | +void ff_ref_idct(short *block) | |
| 94 | +{ | |
| 95 | + /* implement the equation: block = (coefficients') * block * coefficients */ | |
| 96 | + | |
| 97 | + unsigned int i, j, k; | |
| 98 | + double out[8 * 8]; | |
| 99 | + | |
| 100 | + /* out = block * coefficients */ | |
| 101 | + for (i = 0; i < 64; i += 8) { | |
| 102 | + for (j = 0; j < 8; ++j) { | |
| 103 | + double tmp = 0; | |
| 104 | + for (k = 0; k < 8; ++k) { | |
| 105 | + tmp += block[i + k] * coefficients[k * 8 + j]; | |
| 106 | + } | |
| 107 | + out[i + j] = tmp; | |
| 108 | + } | |
| 109 | + } | |
| 110 | + | |
| 111 | + /* block = (coefficients') * out */ | |
| 112 | + for (i = 0; i < 8; ++i) { | |
| 113 | + for (j = 0; j < 8; ++j) { | |
| 114 | + double tmp = 0; | |
| 115 | + for (k = 0; k < 64; k += 8) { | |
| 116 | + tmp += coefficients[k + i] * out[k + j]; | |
| 117 | + } | |
| 118 | + block[i * 8 + j] = floor(tmp + 0.5); | |
| 119 | + } | |
| 120 | + } | |
| 121 | +} | |