2 * reference discrete cosine transform (double precision)
3 * Copyright (C) 2009 Dylan Yudaken
5 * This file is part of FFmpeg.
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.
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.
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
24 * reference discrete cosine transform (double precision)
26 * @author Dylan Yudaken (dyudaken at gmail)
28 * @note This file could be optimized a lot, but is for
29 * reference and so readability is better.
32 #include "libavutil/mathematics.h"
35 static double coefficients
[8 * 8];
38 * Initialize the double precision discrete cosine transform
39 * functions fdct & idct.
41 av_cold
void ff_ref_dct_init(void)
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);
54 * Transform 8x8 block of data with a double precision forward DCT <br>
55 * This is a reference implementation.
57 * @param block pointer to 8x8 block of data to transform
59 void ff_ref_fdct(short *block
)
61 /* implement the equation: block = coefficients * block * coefficients' */
66 /* out = coefficients * block */
67 for (i
= 0; i
< 64; i
+= 8) {
68 for (j
= 0; j
< 8; ++j
) {
70 for (k
= 0; k
< 8; ++k
) {
71 tmp
+= coefficients
[i
+ k
] * block
[k
* 8 + j
];
77 /* block = out * (coefficients') */
78 for (j
= 0; j
< 8; ++j
) {
79 for (i
= 0; i
< 64; i
+= 8) {
81 for (k
= 0; k
< 8; ++k
) {
82 tmp
+= out
[i
+ k
] * coefficients
[j
* 8 + k
];
84 block
[i
+ j
] = floor(tmp
+ 0.499999999999);
90 * Transform 8x8 block of data with a double precision inverse DCT <br>
91 * This is a reference implementation.
93 * @param block pointer to 8x8 block of data to transform
95 void ff_ref_idct(short *block
)
97 /* implement the equation: block = (coefficients') * block * coefficients */
102 /* out = block * coefficients */
103 for (i
= 0; i
< 64; i
+= 8) {
104 for (j
= 0; j
< 8; ++j
) {
106 for (k
= 0; k
< 8; ++k
) {
107 tmp
+= block
[i
+ k
] * coefficients
[k
* 8 + j
];
113 /* block = (coefficients') * out */
114 for (i
= 0; i
< 8; ++i
) {
115 for (j
= 0; j
< 8; ++j
) {
117 for (k
= 0; k
< 64; k
+= 8) {
118 tmp
+= coefficients
[k
+ i
] * out
[k
+ j
];
120 block
[i
* 8 + j
] = floor(tmp
+ 0.5);