FFmpeg
 All Data Structures Namespaces Files Functions Variables Typedefs Enumerations Enumerator Macros Groups Pages
dsd_tablegen.h
Go to the documentation of this file.
1 /*
2  * Header file for hardcoded DSD tables
3  * based on BSD licensed dsd2pcm by Sebastian Gesemann
4  * Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved.
5  *
6  * This file is part of FFmpeg.
7  *
8  * FFmpeg is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * FFmpeg is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with FFmpeg; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #ifndef AVCODEC_DSD_TABLEGEN_H
24 #define AVCODEC_DSD_TABLEGEN_H
25 
26 #include <stdint.h>
27 #include "libavutil/attributes.h"
28 
29 #define HTAPS 48 /** number of FIR constants */
30 #define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */
31 
32 #if CONFIG_HARDCODED_TABLES
33 #define dsd_ctables_tableinit()
34 #include "libavcodec/dsd_tables.h"
35 #else
36 #include "libavutil/common.h"
37 
38 /*
39  * Properties of this 96-tap lowpass filter when applied on a signal
40  * with sampling rate of 44100*64 Hz:
41  *
42  * () has a delay of 17 microseconds.
43  *
44  * () flat response up to 48 kHz
45  *
46  * () if you downsample afterwards by a factor of 8, the
47  * spectrum below 70 kHz is practically alias-free.
48  *
49  * () stopband rejection is about 160 dB
50  *
51  * The coefficient tables ("ctables") take only 6 Kibi Bytes and
52  * should fit into a modern processor's fast cache.
53  */
54 
55 /**
56  * The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter
57  */
58 static const double htaps[HTAPS] = {
59  0.09950731974056658, 0.09562845727714668, 0.08819647126516944,
60  0.07782552527068175, 0.06534876523171299, 0.05172629311427257,
61  0.0379429484910187, 0.02490921351762261, 0.0133774746265897,
62  0.003883043418804416, -0.003284703416210726, -0.008080250212687497,
63  -0.01067241812471033, -0.01139427235000863, -0.0106813877974587,
64  -0.009007905078766049, -0.006828859761015335, -0.004535184322001496,
65  -0.002425035959059578, -0.0006922187080790708, 0.0005700762133516592,
66  0.001353838005269448, 0.001713709169690937, 0.001742046839472948,
67  0.001545601648013235, 0.001226696225277855, 0.0008704322683580222,
68  0.0005381636200535649, 0.000266446345425276, 7.002968738383528e-05,
69  -5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895,
70  -0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05,
71  -4.07492895872535e-05, -2.17407957554587e-05, -9.163058931391722e-06,
72  -2.017460145032201e-06, 1.249721855219005e-06, 2.166655190537392e-06,
73  1.930520892991082e-06, 1.319400334374195e-06, 7.410039764949091e-07,
74  3.423230509967409e-07, 1.244182214744588e-07, 3.130441005359396e-08
75 };
76 
77 static float ctables[CTABLES][256];
78 
79 static av_cold void dsd_ctables_tableinit(void)
80 {
81  int t, e, m, k;
82  double acc;
83  for (t = 0; t < CTABLES; ++t) {
84  k = FFMIN(HTAPS - t * 8, 8);
85  for (e = 0; e < 256; ++e) {
86  acc = 0.0;
87  for (m = 0; m < k; ++m)
88  acc += (((e >> (7 - m)) & 1) * 2 - 1) * htaps[t * 8 + m];
89  ctables[CTABLES - 1 - t][e] = (float)acc;
90  }
91  }
92 }
93 #endif /* CONFIG_HARDCODED_TABLES */
94 
95 #endif /* AVCODEC_DSD_TABLEGEN_H */