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1 | /* | ||
2 | * Direct Stream Digital (DSD) decoder | ||
3 | * based on BSD licensed dsd2pcm by Sebastian Gesemann | ||
4 | * Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved. | ||
5 | * Copyright (c) 2014 Peter Ross | ||
6 | * | ||
7 | * This file is part of FFmpeg. | ||
8 | * | ||
9 | * FFmpeg is free software; you can redistribute it and/or | ||
10 | * modify it under the terms of the GNU Lesser General Public | ||
11 | * License as published by the Free Software Foundation; either | ||
12 | * version 2.1 of the License, or (at your option) any later version. | ||
13 | * | ||
14 | * FFmpeg is distributed in the hope that it will be useful, | ||
15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
17 | * Lesser General Public License for more details. | ||
18 | * | ||
19 | * You should have received a copy of the GNU Lesser General Public | ||
20 | * License along with FFmpeg; if not, write to the Free Software | ||
21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | ||
22 | */ | ||
23 | |||
24 | #include <string.h> | ||
25 | #include "libavutil/attributes.h" | ||
26 | #include "libavutil/reverse.h" | ||
27 | #include "libavutil/thread.h" | ||
28 | #include "dsd.h" | ||
29 | |||
30 | #define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */ | ||
31 | |||
32 | /* | ||
33 | * Properties of this 96-tap lowpass filter when applied on a signal | ||
34 | * with sampling rate of 44100*64 Hz: | ||
35 | * | ||
36 | * () has a delay of 17 microseconds. | ||
37 | * | ||
38 | * () flat response up to 48 kHz | ||
39 | * | ||
40 | * () if you downsample afterwards by a factor of 8, the | ||
41 | * spectrum below 70 kHz is practically alias-free. | ||
42 | * | ||
43 | * () stopband rejection is about 160 dB | ||
44 | * | ||
45 | * The coefficient tables ("ctables") take only 6 Kibi Bytes and | ||
46 | * should fit into a modern processor's fast cache. | ||
47 | */ | ||
48 | |||
49 | /** | ||
50 | * The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter | ||
51 | */ | ||
52 | static const double htaps[HTAPS] = { | ||
53 | 0.09950731974056658, 0.09562845727714668, 0.08819647126516944, | ||
54 | 0.07782552527068175, 0.06534876523171299, 0.05172629311427257, | ||
55 | 0.0379429484910187, 0.02490921351762261, 0.0133774746265897, | ||
56 | 0.003883043418804416, -0.003284703416210726, -0.008080250212687497, | ||
57 | -0.01067241812471033, -0.01139427235000863, -0.0106813877974587, | ||
58 | -0.009007905078766049, -0.006828859761015335, -0.004535184322001496, | ||
59 | -0.002425035959059578, -0.0006922187080790708, 0.0005700762133516592, | ||
60 | 0.001353838005269448, 0.001713709169690937, 0.001742046839472948, | ||
61 | 0.001545601648013235, 0.001226696225277855, 0.0008704322683580222, | ||
62 | 0.0005381636200535649, 0.000266446345425276, 7.002968738383528e-05, | ||
63 | -5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895, | ||
64 | -0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05, | ||
65 | -4.07492895872535e-05, -2.17407957554587e-05, -9.163058931391722e-06, | ||
66 | -2.017460145032201e-06, 1.249721855219005e-06, 2.166655190537392e-06, | ||
67 | 1.930520892991082e-06, 1.319400334374195e-06, 7.410039764949091e-07, | ||
68 | 3.423230509967409e-07, 1.244182214744588e-07, 3.130441005359396e-08 | ||
69 | }; | ||
70 | |||
71 | static float ctables[CTABLES][256]; | ||
72 | |||
73 | 36 | static av_cold void dsd_ctables_tableinit(void) | |
74 | { | ||
75 | int t, e, m, sign; | ||
76 | double acc[CTABLES]; | ||
77 |
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9252 | for (e = 0; e < 256; ++e) { |
78 | 9216 | memset(acc, 0, sizeof(acc)); | |
79 |
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82944 | for (m = 0; m < 8; ++m) { |
80 | 73728 | sign = (((e >> (7 - m)) & 1) * 2 - 1); | |
81 |
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516096 | for (t = 0; t < CTABLES; ++t) |
82 | 442368 | acc[t] += sign * htaps[t * 8 + m]; | |
83 | } | ||
84 |
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64512 | for (t = 0; t < CTABLES; ++t) |
85 | 55296 | ctables[CTABLES - 1 - t][e] = acc[t]; | |
86 | } | ||
87 | 36 | } | |
88 | |||
89 | 68 | av_cold void ff_init_dsd_data(void) | |
90 | { | ||
91 | static AVOnce init_static_once = AV_ONCE_INIT; | ||
92 | 68 | ff_thread_once(&init_static_once, dsd_ctables_tableinit); | |
93 | 68 | } | |
94 | |||
95 | 20 | void ff_dsd2pcm_translate(DSDContext* s, size_t samples, int lsbf, | |
96 | const uint8_t *src, ptrdiff_t src_stride, | ||
97 | float *dst, ptrdiff_t dst_stride) | ||
98 | { | ||
99 | uint8_t buf[FIFOSIZE]; | ||
100 | unsigned pos, i; | ||
101 | uint8_t* p; | ||
102 | double sum; | ||
103 | |||
104 | 20 | pos = s->pos; | |
105 | |||
106 | 20 | memcpy(buf, s->buf, sizeof(buf)); | |
107 | |||
108 |
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94100 | while (samples-- > 0) { |
109 |
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94080 | buf[pos] = lsbf ? ff_reverse[*src] : *src; |
110 | 94080 | src += src_stride; | |
111 | |||
112 | 94080 | p = buf + ((pos - CTABLES) & FIFOMASK); | |
113 | 94080 | *p = ff_reverse[*p]; | |
114 | |||
115 | 94080 | sum = 0.0; | |
116 |
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658560 | for (i = 0; i < CTABLES; i++) { |
117 | 564480 | uint8_t a = buf[(pos - i) & FIFOMASK]; | |
118 | 564480 | uint8_t b = buf[(pos - (CTABLES*2 - 1) + i) & FIFOMASK]; | |
119 | 564480 | sum += ctables[i][a] + ctables[i][b]; | |
120 | } | ||
121 | |||
122 | 94080 | *dst = (float)sum; | |
123 | 94080 | dst += dst_stride; | |
124 | |||
125 | 94080 | pos = (pos + 1) & FIFOMASK; | |
126 | } | ||
127 | |||
128 | 20 | s->pos = pos; | |
129 | 20 | memcpy(s->buf, buf, sizeof(buf)); | |
130 | 20 | } | |
131 |