| 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 |
| 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 | #include "dctref.h" |
| 34 | |
| 35 | static double coefficients[8 * 8]; |
| 36 | |
| 37 | /** |
| 38 | * Initialize the double precision discrete cosine transform |
| 39 | * functions fdct & idct. |
| 40 | */ |
| 41 | av_cold void ff_ref_dct_init(void) |
| 42 | { |
| 43 | unsigned int i, j; |
| 44 | |
| 45 | for (j = 0; j < 8; ++j) { |
| 46 | coefficients[j] = sqrt(0.125); |
| 47 | for (i = 8; i < 64; i += 8) { |
| 48 | coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0); |
| 49 | } |
| 50 | } |
| 51 | } |
| 52 | |
| 53 | /** |
| 54 | * Transform 8x8 block of data with a double precision forward DCT <br> |
| 55 | * This is a reference implementation. |
| 56 | * |
| 57 | * @param block pointer to 8x8 block of data to transform |
| 58 | */ |
| 59 | void ff_ref_fdct(short *block) |
| 60 | { |
| 61 | /* implement the equation: block = coefficients * block * coefficients' */ |
| 62 | |
| 63 | unsigned int i, j, k; |
| 64 | double out[8 * 8]; |
| 65 | |
| 66 | /* out = coefficients * block */ |
| 67 | for (i = 0; i < 64; i += 8) { |
| 68 | for (j = 0; j < 8; ++j) { |
| 69 | double tmp = 0; |
| 70 | for (k = 0; k < 8; ++k) { |
| 71 | tmp += coefficients[i + k] * block[k * 8 + j]; |
| 72 | } |
| 73 | out[i + j] = tmp * 8; |
| 74 | } |
| 75 | } |
| 76 | |
| 77 | /* block = out * (coefficients') */ |
| 78 | for (j = 0; j < 8; ++j) { |
| 79 | for (i = 0; i < 64; i += 8) { |
| 80 | double tmp = 0; |
| 81 | for (k = 0; k < 8; ++k) { |
| 82 | tmp += out[i + k] * coefficients[j * 8 + k]; |
| 83 | } |
| 84 | block[i + j] = floor(tmp + 0.499999999999); |
| 85 | } |
| 86 | } |
| 87 | } |
| 88 | |
| 89 | /** |
| 90 | * Transform 8x8 block of data with a double precision inverse DCT <br> |
| 91 | * This is a reference implementation. |
| 92 | * |
| 93 | * @param block pointer to 8x8 block of data to transform |
| 94 | */ |
| 95 | void ff_ref_idct(short *block) |
| 96 | { |
| 97 | /* implement the equation: block = (coefficients') * block * coefficients */ |
| 98 | |
| 99 | unsigned int i, j, k; |
| 100 | double out[8 * 8]; |
| 101 | |
| 102 | /* out = block * coefficients */ |
| 103 | for (i = 0; i < 64; i += 8) { |
| 104 | for (j = 0; j < 8; ++j) { |
| 105 | double tmp = 0; |
| 106 | for (k = 0; k < 8; ++k) { |
| 107 | tmp += block[i + k] * coefficients[k * 8 + j]; |
| 108 | } |
| 109 | out[i + j] = tmp; |
| 110 | } |
| 111 | } |
| 112 | |
| 113 | /* block = (coefficients') * out */ |
| 114 | for (i = 0; i < 8; ++i) { |
| 115 | for (j = 0; j < 8; ++j) { |
| 116 | double tmp = 0; |
| 117 | for (k = 0; k < 64; k += 8) { |
| 118 | tmp += coefficients[k + i] * out[k + j]; |
| 119 | } |
| 120 | block[i * 8 + j] = floor(tmp + 0.5); |
| 121 | } |
| 122 | } |
| 123 | } |