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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 | |
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 | } |