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 */
58static 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
77static float ctables[CTABLES][256];
78
79static 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 */
96