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
35static double coefficients[8 * 8];
36
37/**
38 * Initialize the double precision discrete cosine transform
39 * functions fdct & idct.
40 */
41av_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 */
59void 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 */
95void 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