blob: 851014b664ab19298954c83c24eab1dcbdecf9eb
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 | } |
124 |