FFmpeg: libavcodec/dsd.c Source File

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dsd.c

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1 /*

2 * Direct Stream Digital (DSD) decoder

3 * based on BSD licensed dsd2pcm by Sebastian Gesemann

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 */

24 #include <string.h>

25 #include "libavutil/attributes.h"

26 #include "libavutil/reverse.h"

27 #include "libavutil/thread.h"

28 #include "dsd.h"

30 #define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */

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 */

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 };

71 static float ctables[CTABLES][256];

73 static av_cold void dsd_ctables_tableinit(void)

74 {

75 int t, e, m, sign;

76 double acc[CTABLES];

77 for (e = 0; e < 256; ++e) {

78 memset(acc, 0, sizeof(acc));

79 for (m = 0; m < 8; ++m) {

80 sign = (((e >> (7 - m)) & 1) * 2 - 1);

81 for (t = 0; t < CTABLES; ++t)

82 acc[t] += sign * htaps[t * 8 + m];

83 }

84 for (t = 0; t < CTABLES; ++t)

85 ctables[CTABLES - 1 - t][e] = acc[t];

86 }

87 }

89 av_cold void ff_init_dsd_data(void)

90 {

91 static AVOnce init_static_once = AV_ONCE_INIT;

92 ff_thread_once(&init_static_once, dsd_ctables_tableinit);

93 }

95 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 pos = s->pos;

105

106 memcpy(buf, s->buf, sizeof(buf));

107

108 while (samples-- > 0) {

109 buf[pos] = lsbf ? ff_reverse[*src] : *src;

110 src += src_stride;

111

112 p = buf + ((pos - CTABLES) & FIFOMASK);

113 *p = ff_reverse[*p];

114

115 sum = 0.0;

116 for (i = 0; i < CTABLES; i++) {

117 uint8_t a = buf[(pos - i) & FIFOMASK];

118 uint8_t b = buf[(pos - (CTABLES*2 - 1) + i) & FIFOMASK];

119 sum += ctables[i][a] + ctables[i][b];

120 }

121

122 *dst = (float)sum;

123 dst += dst_stride;

124

125 pos = (pos + 1) & FIFOMASK;

126 }

127

128 s->pos = pos;

129 memcpy(s->buf, buf, sizeof(buf));

130 }

acc

int acc

Definition: yuv2rgb.c:554

ctables

static float ctables[CTABLES][256]

Definition: dsd.c:71

thread.h

#define b

Definition: input.c:41

ff_reverse

const uint8_t ff_reverse[256]

Definition: reverse.c:23

reverse.h

dsd.h

CTABLES

#define CTABLES

Definition: dsd.c:30

FIFOMASK

#define FIFOMASK

Definition: dsd.h:32

ff_thread_once

static int ff_thread_once(char *control, void(*routine)(void))

Definition: thread.h:184

av_cold

#define av_cold

Definition: attributes.h:90

float

Definition: af_crystalizer.c:122

#define s(width, name)

Definition: cbs_vp9.c:256

htaps

static const double htaps[HTAPS]

The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter.

Definition: dsd.c:52

AV_ONCE_INIT

#define AV_ONCE_INIT

Definition: thread.h:182

AVOnce

#define AVOnce

Definition: thread.h:181

ff_init_dsd_data

av_cold void ff_init_dsd_data(void)

Definition: dsd.c:89

HTAPS

#define HTAPS

Definition: dsd.h:30

The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a

Definition: undefined.txt:41

attributes.h

#define i(width, name, range_min, range_max)

Definition: cbs_h2645.c:269

dsd_ctables_tableinit

static av_cold void dsd_ctables_tableinit(void)

Definition: dsd.c:73

DSDContext

Per-channel buffer.

Definition: dsd.h:41

ff_dsd2pcm_translate

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)