aecd63478e
This is possible by not converting from LSBF to MSBF; instead add LSBF LUTs. This approach necessitates reversing the initial values. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
135 lines
4.6 KiB
C
135 lines
4.6 KiB
C
/*
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* Direct Stream Digital (DSD) decoder
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* based on BSD licensed dsd2pcm by Sebastian Gesemann
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* Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved.
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* Copyright (c) 2014 Peter Ross
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <string.h>
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#include "libavutil/attributes.h"
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#include "libavutil/reverse.h"
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#include "libavutil/thread.h"
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#include "dsd.h"
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#define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */
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/*
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* Properties of this 96-tap lowpass filter when applied on a signal
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* with sampling rate of 44100*64 Hz:
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*
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* () has a delay of 17 microseconds.
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*
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* () flat response up to 48 kHz
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*
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* () if you downsample afterwards by a factor of 8, the
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* spectrum below 70 kHz is practically alias-free.
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*
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* () stopband rejection is about 160 dB
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*
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* The coefficient tables ("ctables") take only 6 Kibi Bytes and
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* should fit into a modern processor's fast cache.
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*/
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/**
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* The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter
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*/
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static const double htaps[HTAPS] = {
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0.09950731974056658, 0.09562845727714668, 0.08819647126516944,
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0.07782552527068175, 0.06534876523171299, 0.05172629311427257,
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0.0379429484910187, 0.02490921351762261, 0.0133774746265897,
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0.003883043418804416, -0.003284703416210726, -0.008080250212687497,
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-0.01067241812471033, -0.01139427235000863, -0.0106813877974587,
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-0.009007905078766049, -0.006828859761015335, -0.004535184322001496,
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-0.002425035959059578, -0.0006922187080790708, 0.0005700762133516592,
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0.001353838005269448, 0.001713709169690937, 0.001742046839472948,
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0.001545601648013235, 0.001226696225277855, 0.0008704322683580222,
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0.0005381636200535649, 0.000266446345425276, 7.002968738383528e-05,
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-5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895,
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-0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05,
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-4.07492895872535e-05, -2.17407957554587e-05, -9.163058931391722e-06,
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-2.017460145032201e-06, 1.249721855219005e-06, 2.166655190537392e-06,
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1.930520892991082e-06, 1.319400334374195e-06, 7.410039764949091e-07,
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3.423230509967409e-07, 1.244182214744588e-07, 3.130441005359396e-08
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};
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static double ctables_lsbf[CTABLES][256];
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static double ctables_msbf[CTABLES][256];
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static av_cold void dsd_ctables_tableinit(void)
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{
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int t, e, m, sign;
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double acc[CTABLES];
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for (e = 0; e < 256; ++e) {
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memset(acc, 0, sizeof(acc));
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for (m = 0; m < 8; ++m) {
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sign = (((e >> (7 - m)) & 1) * 2 - 1);
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for (t = 0; t < CTABLES; ++t)
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acc[t] += sign * htaps[t * 8 + m];
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}
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for (t = 0; t < CTABLES; ++t) {
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ctables_msbf[CTABLES - 1 - t][e] = acc[t];
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ctables_lsbf[CTABLES - 1 - t][ff_reverse[e]] = acc[t];
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}
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}
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}
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av_cold void ff_init_dsd_data(void)
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{
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static AVOnce init_static_once = AV_ONCE_INIT;
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ff_thread_once(&init_static_once, dsd_ctables_tableinit);
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}
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void ff_dsd2pcm_translate(DSDContext* s, size_t samples, int lsbf,
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const uint8_t *src, ptrdiff_t src_stride,
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float *dst, ptrdiff_t dst_stride)
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{
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uint8_t buf[FIFOSIZE];
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unsigned pos, i;
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uint8_t* p;
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double sum;
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const double (*const ctables)[256] = lsbf ? ctables_lsbf : ctables_msbf;
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pos = s->pos;
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memcpy(buf, s->buf, sizeof(buf));
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while (samples-- > 0) {
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buf[pos] = *src;
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src += src_stride;
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p = buf + ((pos - CTABLES) & FIFOMASK);
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*p = ff_reverse[*p];
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sum = 0.0;
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for (i = 0; i < CTABLES; i++) {
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uint8_t a = buf[(pos - i) & FIFOMASK];
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uint8_t b = buf[(pos - (CTABLES*2 - 1) + i) & FIFOMASK];
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sum += ctables[i][a] + ctables[i][b];
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}
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*dst = (float)sum;
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dst += dst_stride;
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pos = (pos + 1) & FIFOMASK;
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}
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s->pos = pos;
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memcpy(s->buf, buf, sizeof(buf));
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}
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