Resampler.h
/*
* This file is part of libsidplayfp, a SID player engine.
*
* Copyright 2011-2024 Leandro Nini <drfiemost@users.sourceforge.net>
* Copyright 2007-2010 Antti Lankila
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#ifndef RESAMPLER_H
#define RESAMPLER_H
#include <cmath>
#include <cassert>
#include "sidcxx11.h"
#include "siddefs-fp.h"
namespace reSIDfp
{
class Resampler
{
private:
template<int m>
static inline int clipper(int x)
{
assert(x >= 0);
constexpr int threshold = 28000;
if (likely(x < threshold))
return x;
constexpr double max_val = static_cast<double>(m);
constexpr double t = threshold / max_val;
constexpr double a = 1. - t;
constexpr double b = 1. / a;
double value = static_cast<double>(x - threshold) / max_val;
value = t + a * std::tanh(b * value);
return static_cast<int>(value * max_val);
}
/*
* Soft Clipping implementation, splitted for test.
*/
static inline int softClipImpl(int x)
{
return x < 0 ? -clipper<32768>(-x) : clipper<32767>(x);
}
protected:
/*
* Soft Clipping into 16 bit range [-32768,32767]
*/
static inline short softClip(int x) { return static_cast<short>(softClipImpl(x)); }
virtual int output() const = 0;
Resampler() {}
public:
virtual ~Resampler() = default;
virtual bool input(int sample) = 0;
inline short getOutput(int scaleFactor) const
{
const int out = (scaleFactor * output()) / 2;
return softClip(out);
}
virtual void reset() = 0;
};
} // namespace reSIDfp
#endif
reSIDfp::Resampler
Definition Resampler.h:40
reSIDfp::Resampler::input
virtual bool input(int sample)=0
reSIDfp::Resampler::getOutput
short getOutput(int scaleFactor) const
Definition Resampler.h:94