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
|
/*
* Direct Stream Digital (DSD) decoder
* based on BSD licensed dsd2pcm by Sebastian Gesemann
* Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved.
* Copyright (c) 2014 Peter Ross
*
* 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 Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <string.h>
#include "libavutil/attributes.h"
#include "libavutil/reverse.h"
#include "libavutil/thread.h"
#include "dsd.h"
#define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */
/*
* Properties of this 96-tap lowpass filter when applied on a signal
* with sampling rate of 44100*64 Hz:
*
* () has a delay of 17 microseconds.
*
* () flat response up to 48 kHz
*
* () if you downsample afterwards by a factor of 8, the
* spectrum below 70 kHz is practically alias-free.
*
* () stopband rejection is about 160 dB
*
* The coefficient tables ("ctables") take only 6 Kibi Bytes and
* should fit into a modern processor's fast cache.
*/
/**
* The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter
*/
static const double htaps[HTAPS] = {
0.09950731974056658, 0.09562845727714668, 0.08819647126516944,
0.07782552527068175, 0.06534876523171299, 0.05172629311427257,
0.0379429484910187, 0.02490921351762261, 0.0133774746265897,
0.003883043418804416, -0.003284703416210726, -0.008080250212687497,
-0.01067241812471033, -0.01139427235000863, -0.0106813877974587,
-0.009007905078766049, -0.006828859761015335, -0.004535184322001496,
-0.002425035959059578, -0.0006922187080790708, 0.0005700762133516592,
0.001353838005269448, 0.001713709169690937, 0.001742046839472948,
0.001545601648013235, 0.001226696225277855, 0.0008704322683580222,
0.0005381636200535649, 0.000266446345425276, 7.002968738383528e-05,
-5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895,
-0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05,
-4.07492895872535e-05, -2.17407957554587e-05, -9.163058931391722e-06,
-2.017460145032201e-06, 1.249721855219005e-06, 2.166655190537392e-06,
1.930520892991082e-06, 1.319400334374195e-06, 7.410039764949091e-07,
3.423230509967409e-07, 1.244182214744588e-07, 3.130441005359396e-08
};
static float ctables[CTABLES][256];
static av_cold void dsd_ctables_tableinit(void)
{
int t, e, m, sign;
double acc[CTABLES];
for (e = 0; e < 256; ++e) {
memset(acc, 0, sizeof(acc));
for (m = 0; m < 8; ++m) {
sign = (((e >> (7 - m)) & 1) * 2 - 1);
for (t = 0; t < CTABLES; ++t)
acc[t] += sign * htaps[t * 8 + m];
}
for (t = 0; t < CTABLES; ++t)
ctables[CTABLES - 1 - t][e] = acc[t];
}
}
av_cold void ff_init_dsd_data(void)
{
static AVOnce init_static_once = AV_ONCE_INIT;
ff_thread_once(&init_static_once, dsd_ctables_tableinit);
}
void ff_dsd2pcm_translate(DSDContext* s, size_t samples, int lsbf,
const uint8_t *src, ptrdiff_t src_stride,
float *dst, ptrdiff_t dst_stride)
{
uint8_t buf[FIFOSIZE];
unsigned pos, i;
uint8_t* p;
double sum;
pos = s->pos;
memcpy(buf, s->buf, sizeof(buf));
while (samples-- > 0) {
buf[pos] = lsbf ? ff_reverse[*src] : *src;
src += src_stride;
p = buf + ((pos - CTABLES) & FIFOMASK);
*p = ff_reverse[*p];
sum = 0.0;
for (i = 0; i < CTABLES; i++) {
uint8_t a = buf[(pos - i) & FIFOMASK];
uint8_t b = buf[(pos - (CTABLES*2 - 1) + i) & FIFOMASK];
sum += ctables[i][a] + ctables[i][b];
}
*dst = (float)sum;
dst += dst_stride;
pos = (pos + 1) & FIFOMASK;
}
s->pos = pos;
memcpy(s->buf, buf, sizeof(buf));
}
|
