falpha_branch.cpp

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// SPDX-License-Identifier: GPL-2.0-only
//
// Copyright (c) 2006-2008 Marc Brooker and Michael Inggs
// Copyright (c) 2008-present FERS Contributors (see AUTHORS.md).
//
// See the GNU GPLv2 LICENSE file in the FERS project root for more information.
 
/**
 * @file falpha_branch.cpp
 * @brief Implementation of the FAlphaBranch class for noise generation.
 */
 
#include "falpha_branch.h"
 
#include <array>
#include <cmath>
#include <span>
#include <stdexcept>
#include <utility>
 
#include "core/logging.h"
#include "signal/dsp_filters.h"
 
using fers_signal::DecadeUpsampler;
using fers_signal::IirFilter;
using logging::Level;
 
namespace noise
{
    FAlphaBranch::FAlphaBranch(std::mt19937& rngEngine, RealType ffrac, unsigned fint,
                               std::unique_ptr<FAlphaBranch> pre, const bool last) :
        _rng_engine_ref(rngEngine), _normal_dist{0.0, 1.0}, _pre(std::move(pre)), _buffer(10), _ffrac(ffrac),
        _fint(fint), _last(last)
    {
        LOG(Level::TRACE, "Creating FAlphaBranch: ffrac={} fint={}", ffrac, fint);
        _upsample_scale = std::pow(10, ffrac + fint + 0.5);
        init();
 
        if (!_last)
        {
            refill();
        }
    }
 
    void FAlphaBranch::init()
    {
        _upsampler = std::make_unique<DecadeUpsampler>();
 
        if (_pre)
        {
            constexpr std::array hp_num = {3.817871081981451e-01,  -4.093384095523618e+00, 2.005300512623078e+01,
                                           -5.924672881811163e+01, 1.172948159891025e+02,  -1.633810410083022e+02,
                                           1.633810410083034e+02,  -1.172948159891052e+02, 5.924672881811390e+01,
                                           -2.005300512623186e+01, 4.093384095523903e+00,  -3.817871081981776e-01};
            constexpr std::array hp_den = {1.000000000000000e+00,  -8.829695665523831e+00, 3.583068809011030e+01,
                                           -8.811479652970442e+01, 1.457874067329429e+02,  -1.702715637111961e+02,
                                           1.431504350055831e+02,  -8.656925883534657e+01, 3.687395592491803e+01,
                                           -1.052413841411803e+01, 1.808292123637038e+00,  -1.412932578340511e-01};
            _highpass = std::make_unique<IirFilter>(hp_den.data(), hp_num.data(), hp_num.size());
        }
 
        if (_ffrac == 0.5f)
        {
            constexpr std::array sf_num = {
                5.210373977738306e-03,  -7.694671394585578e-03, 1.635979377907092e-03,  9.852449140857658e-05,
                -2.080553126780113e-03, 4.088764157029523e-03,  -1.549082440084623e-03, 9.054734252370680e-04,
                -3.467369912368729e-04, 4.516383087838856e-04,  -1.063356106118517e-03, 1.330008998057684e-04,
                6.556909567323943e-04,  -4.839476350293955e-04, 6.664936170526832e-05,  1.528520559763056e-05};
            constexpr std::array sf_den = {
                1.000000000000000e+00,  -2.065565041154101e+00, 1.130909190864681e+00,  -1.671244644503288e-01,
                -3.331474931013877e-01, 9.952625337612708e-01,  -7.123036343635182e-01, 3.297062696290504e-01,
                -1.925691520710595e-01, 1.301247006176314e-01,  -2.702016290409912e-01, 1.455380885858886e-01,
                1.091921868353888e-01,  -1.524953111510459e-01, 5.667716332023935e-02,  -2.890314873767405e-03};
            _shape_gain = 5.210373977738306e-03;
            _shape_filter = std::make_unique<IirFilter>(sf_den.data(), sf_num.data(), sf_num.size());
        }
        else if (_ffrac != 0.0f)
        {
            LOG(Level::FATAL, "Fractional noise generation values other than 0.5 or 0 are not supported. ffrac={}",
                _ffrac);
            throw std::runtime_error("Fractional integrator values other than 0.5 or 0 are not supported");
        }
 
        if (_fint > 0)
        {
            _integ_gain = 1.0f;
 
            if (_fint == 1)
            {
                constexpr std::array<RealType, 2> i_den = {1.0f, -1.0f};
                constexpr std::array<RealType, 2> i_num = {1.0f, 0.0f};
                _integ_filter = std::make_unique<IirFilter>(i_den.data(), i_num.data(), i_num.size());
            }
            else if (_fint == 2)
            {
                constexpr std::array<RealType, 3> i_den = {1.0f, -2.0f, 1.0f};
                constexpr std::array<RealType, 3> i_num = {1.0f, 0.0f, 0.0f};
                _integ_filter = std::make_unique<IirFilter>(i_den.data(), i_num.data(), i_num.size());
            }
            else
            {
                throw std::runtime_error("Only alpha values between 2 and -2 are supported for noise generation");
            }
        }
        _offset_sample = 0.0f;
        _got_offset = false;
    }
 
    RealType FAlphaBranch::getSample() noexcept
    {
        if (!_last)
        {
            const RealType ret = _buffer[_buffer_samples++];
            if (_buffer_samples == 10)
            {
                refill();
            }
            return ret;
        }
        return calcSample() + _offset_sample * _upsample_scale;
    }
 
    RealType FAlphaBranch::calcSample() noexcept
    {
        RealType sample = _normal_dist(_rng_engine_ref.get());
 
        if (_shape_filter)
        {
            sample = _shape_filter->filter(sample) / _shape_gain;
        }
 
        if (_integ_filter)
        {
            sample = _integ_filter->filter(sample) / _integ_gain;
        }
 
        if (_pre)
        {
            sample = _highpass->filter(sample);
            if (_got_offset)
            {
                sample += _pre->getSample() * _pre_scale - _offset_sample;
            }
            else
            {
                _got_offset = true;
                _offset_sample = _pre->getSample() * _pre_scale;
            }
        }
 
        return sample;
    }
 
    void FAlphaBranch::refill() noexcept
    {
        const RealType sample = calcSample();
        _upsampler->upsample(sample, _buffer);
 
        for (auto& value : _buffer)
        {
            value *= _upsample_scale;
            value += _offset_sample;
        }
 
        _buffer_samples = 0;
    }
 
    void FAlphaBranch::flush(const RealType scale)
    {
        init();
        _pre_scale = scale;
    }
}