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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 */ |