love2d.megasource/libs/openal-soft/utils/makemhr/makemhr.h

#ifndef MAKEMHR_H
#define MAKEMHR_H

#include <algorithm>
#include <array>
#include <complex>
#include <vector>

#include "alcomplex.h"
#include "alspan.h"
#include "polyphase_resampler.h"


// The maximum path length used when processing filenames.
inline constexpr auto MAX_PATH_LEN = 256u;

// The limit to the number of 'distances' listed in the data set definition.
// Must be less than 256
inline constexpr auto MAX_FD_COUNT = 16u;

// The limits to the number of 'elevations' listed in the data set definition.
// Must be less than 256.
inline constexpr auto MIN_EV_COUNT = 5u;
inline constexpr auto MAX_EV_COUNT = 181u;

// The limits for each of the 'azimuths' listed in the data set definition.
// Must be less than 256.
inline constexpr auto MIN_AZ_COUNT = 1u;
inline constexpr auto MAX_AZ_COUNT = 255u;

// The limits for the 'distance' from source to listener for each field in
// the definition file.
inline constexpr auto MIN_DISTANCE = 0.05;
inline constexpr auto MAX_DISTANCE = 2.50;

// The limits for the sample 'rate' metric in the data set definition and for
// resampling.
inline constexpr auto MIN_RATE = 32000u;
inline constexpr auto MAX_RATE = 96000u;

// The limits for the HRIR 'points' metric in the data set definition.
inline constexpr auto MIN_POINTS = 16u;
inline constexpr auto MAX_POINTS = 8192u;


using uint = unsigned int;

/* Complex double type. */
using complex_d = std::complex<double>;


enum ChannelModeT : bool {
    CM_AllowStereo = false,
    CM_ForceMono = true
};

// Sample and channel type enum values.
enum SampleTypeT {
    ST_S16 = 0,
    ST_S24 = 1
};

// Certain iterations rely on these integer enum values.
enum ChannelTypeT {
    CT_NONE   = -1,
    CT_MONO   = 0,
    CT_STEREO = 1
};

// Structured HRIR storage for stereo azimuth pairs, elevations, and fields.
struct HrirAzT {
    double mAzimuth{0.0};
    uint mIndex{0u};
    std::array<double,2> mDelays{};
    std::array<al::span<double>,2> mIrs{};
};

struct HrirEvT {
    double mElevation{0.0};
    al::span<HrirAzT> mAzs;
};

struct HrirFdT {
    double mDistance{0.0};
    uint mEvStart{0u};
    al::span<HrirEvT> mEvs;
};

// The HRIR metrics and data set used when loading, processing, and storing
// the resulting HRTF.
struct HrirDataT {
    uint mIrRate{0u};
    SampleTypeT mSampleType{ST_S24};
    ChannelTypeT mChannelType{CT_NONE};
    uint mIrPoints{0u};
    uint mFftSize{0u};
    uint mIrSize{0u};
    double mRadius{0.0};
    uint mIrCount{0u};

    std::vector<double> mHrirsBase;
    std::vector<HrirEvT> mEvsBase;
    std::vector<HrirAzT> mAzsBase;

    std::vector<HrirFdT> mFds;

    /* GCC warns when it tries to inline this. */
    ~HrirDataT();
};


bool PrepareHrirData(const al::span<const double> distances,
    const al::span<const uint,MAX_FD_COUNT> evCounts,
    const al::span<const std::array<uint,MAX_EV_COUNT>,MAX_FD_COUNT> azCounts, HrirDataT *hData);

/* Calculate the magnitude response of the given input.  This is used in
 * place of phase decomposition, since the phase residuals are discarded for
 * minimum phase reconstruction.  The mirrored half of the response is also
 * discarded.
 */
inline void MagnitudeResponse(const al::span<const complex_d> in, const al::span<double> out)
{
    static constexpr double Epsilon{1e-9};
    for(size_t i{0};i < out.size();++i)
        out[i] = std::max(std::abs(in[i]), Epsilon);
}

// Performs a forward FFT.
inline void FftForward(const uint n, complex_d *inout)
{ forward_fft(al::span{inout, n}); }

// Performs an inverse FFT, scaling the result by the number of elements.
inline void FftInverse(const uint n, complex_d *inout)
{
    const auto values = al::span{inout, n};
    inverse_fft(values);

    const double f{1.0 / n};
    std::for_each(values.begin(), values.end(), [f](complex_d &value) { value *= f; });
}

// Performs linear interpolation.
inline double Lerp(const double a, const double b, const double f)
{ return a + f * (b - a); }

#endif /* MAKEMHR_H */