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 */ 52static 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 71static float ctables[CTABLES][256]; 72 73static 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 89av_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 95void 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} 131