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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 | } | ||