1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
|
/*
* (I)DCT Transforms
* Copyright (c) 2009 Peter Ross <pross@xvid.org>
* Copyright (c) 2010 Alex Converse <alex.converse@gmail.com>
* Copyright (c) 2010 Vitor Sessak
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file libavcodec/dct.c
* (Inverse) Discrete Cosine Transforms. These are also known as the
* type II and type III DCTs respectively.
*/
#include <math.h>
#include "libavutil/mathematics.h"
#include "fft.h"
av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
{
int n = 1 << nbits;
int i;
s->nbits = nbits;
s->inverse = inverse;
ff_init_ff_cos_tabs(nbits+2);
s->costab = ff_cos_tabs[nbits+2];
s->csc2 = av_malloc(n/2 * sizeof(FFTSample));
if (ff_rdft_init(&s->rdft, nbits, inverse) < 0) {
av_free(s->csc2);
return -1;
}
for (i = 0; i < n/2; i++)
s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1)));
return 0;
}
/* sin((M_PI * x / (2*n)) */
#define SIN(s,n,x) (s->costab[(n) - (x)])
/* cos((M_PI * x / (2*n)) */
#define COS(s,n,x) (s->costab[x])
static void ff_dct_calc_c(DCTContext *ctx, FFTSample *data)
{
int n = 1 << ctx->nbits;
int i;
if (ctx->inverse) {
float next = data[n - 1];
float inv_n = 1.0f / n;
for (i = n - 2; i >= 2; i -= 2) {
float val1 = data[i ];
float val2 = data[i - 1] - data[i + 1];
float c = COS(ctx, n, i);
float s = SIN(ctx, n, i);
data[i ] = c * val1 + s * val2;
data[i + 1] = s * val1 - c * val2;
}
data[1] = 2 * next;
ff_rdft_calc(&ctx->rdft, data);
for (i = 0; i < n / 2; i++) {
float tmp1 = data[i ] * inv_n;
float tmp2 = data[n - i - 1] * inv_n;
float csc = ctx->csc2[i] * (tmp1 - tmp2);
tmp1 += tmp2;
data[i ] = tmp1 + csc;
data[n - i - 1] = tmp1 - csc;
}
} else {
float next;
for (i=0; i < n/2; i++) {
float tmp1 = data[i ];
float tmp2 = data[n - i - 1];
float s = SIN(ctx, n, 2*i + 1);
s *= tmp1 - tmp2;
tmp1 = (tmp1 + tmp2) * 0.5f;
data[i ] = tmp1 + s;
data[n-i-1] = tmp1 - s;
}
ff_rdft_calc(&ctx->rdft, data);
next = data[1] * 0.5;
data[1] *= -1;
for (i = n - 2; i >= 0; i -= 2) {
float inr = data[i ];
float ini = data[i + 1];
float c = COS(ctx, n, i);
float s = SIN(ctx, n, i);
data[i ] = c * inr + s * ini;
data[i+1] = next;
next += s * inr - c * ini;
}
}
}
void ff_dct_calc(DCTContext *s, FFTSample *data)
{
ff_dct_calc_c(s, data);
}
av_cold void ff_dct_end(DCTContext *s)
{
ff_rdft_end(&s->rdft);
av_free(s->csc2);
}
|
