libavcodec/dsd.c

   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 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 }
  88
  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 }
  94
  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 }