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/*
* Header file for hardcoded DSD tables
* based on BSD licensed dsd2pcm by Sebastian Gesemann
* Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved.
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef AVCODEC_DSD_TABLEGEN_H
#define AVCODEC_DSD_TABLEGEN_H
#include <stdint.h>
#include "libavutil/attributes.h"
#define HTAPS 48 /** number of FIR constants */
#define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */
#if CONFIG_HARDCODED_TABLES
#define dsd_ctables_tableinit()
#include "libavcodec/dsd_tables.h"
#else
#include "libavutil/common.h"
/*
* Properties of this 96-tap lowpass filter when applied on a signal
* with sampling rate of 44100*64 Hz:
*
* () has a delay of 17 microseconds.
*
* () flat response up to 48 kHz
*
* () if you downsample afterwards by a factor of 8, the
* spectrum below 70 kHz is practically alias-free.
*
* () stopband rejection is about 160 dB
*
* The coefficient tables ("ctables") take only 6 Kibi Bytes and
* should fit into a modern processor's fast cache.
*/
/**
* The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter
*/
static const double htaps[HTAPS] = {
0.09950731974056658, 0.09562845727714668, 0.08819647126516944,
0.07782552527068175, 0.06534876523171299, 0.05172629311427257,
0.0379429484910187, 0.02490921351762261, 0.0133774746265897,
0.003883043418804416, -0.003284703416210726, -0.008080250212687497,
-0.01067241812471033, -0.01139427235000863, -0.0106813877974587,
-0.009007905078766049, -0.006828859761015335, -0.004535184322001496,
-0.002425035959059578, -0.0006922187080790708, 0.0005700762133516592,
0.001353838005269448, 0.001713709169690937, 0.001742046839472948,
0.001545601648013235, 0.001226696225277855, 0.0008704322683580222,
0.0005381636200535649, 0.000266446345425276, 7.002968738383528e-05,
-5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895,
-0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05,
-4.07492895872535e-05, -2.17407957554587e-05, -9.163058931391722e-06,
-2.017460145032201e-06, 1.249721855219005e-06, 2.166655190537392e-06,
1.930520892991082e-06, 1.319400334374195e-06, 7.410039764949091e-07,
3.423230509967409e-07, 1.244182214744588e-07, 3.130441005359396e-08
};
static float ctables[CTABLES][256];
static av_cold void dsd_ctables_tableinit(void)
{
int t, e, m, k;
double acc;
for (t = 0; t < CTABLES; ++t) {
k = FFMIN(HTAPS - t * 8, 8);
for (e = 0; e < 256; ++e) {
acc = 0.0;
for (m = 0; m < k; ++m)
acc += (((e >> (7 - m)) & 1) * 2 - 1) * htaps[t * 8 + m];
ctables[CTABLES - 1 - t][e] = (float)acc;
}
}
}
#endif /* CONFIG_HARDCODED_TABLES */
#endif /* AVCODEC_DSD_TABLEGEN_H */
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