EqualTemperament.h

#ifndef MCC_TUNING_EQUAL_TEMPERAMENT_H
#define MCC_TUNING_EQUAL_TEMPERAMENT_H
 
#include <MCC_BuildSettings.h>
 
#include <float.h>
#include <stdint.h>
 
#include <Foundation/Math/Arithmetic.h>
 
#include <MCC/Pitch/PitchClass.h>
#include <MCC/Pitch/Pitch.h>
#include <MCC/Tuning/Tuning.h>
 
namespace MCC {

class EqualTemperament {
    MCC::Tuning _tuning;
 
public:
    constexpr EqualTemperament() noexcept : _tuning() {}

    constexpr explicit EqualTemperament(MCC::Tuning tuning) noexcept
        : _tuning(tuning) {}

    static constexpr EqualTemperament Standard() noexcept {
        return EqualTemperament(MCC::Tuning::Standard());
    }

    constexpr bool IsValid() const noexcept { return _tuning.IsValid(); }

    constexpr MCC::Tuning Tuning() const noexcept { return _tuning; }

    MCC_CONSTEXPR14 float Frequency(MCC::Pitch pitch) const noexcept {
        if (!IsValid() || !pitch.IsValid()) {
            return 0.0f;
        }
 
        // 2^(k / 12) for k = 0..11.
        constexpr float ratios[MCC::PitchClass::Count] = {
            1.0f,
            1.0594630943592953f,
            1.1224620483093730f,
            1.1892071150027210f,
            1.2599210498948732f,
            1.3348398541700344f,
            1.4142135623730951f,
            1.4983070768766815f,
            1.5874010519681994f,
            1.6817928305074290f,
            1.7817974362806785f,
            1.8877486253633870f};
 
        const int32_t distance =
            static_cast<int32_t>(pitch.ChromaticIndex().Value()) -
            _tuning.Reference().ChromaticIndex().Value();
        int32_t octaves = Foundation::Math::FloorDiv(
            distance, MCC::PitchClass::Count);
        const int32_t semitones = Foundation::Math::FloorMod(
            distance, MCC::PitchClass::Count);
 
        float frequency = _tuning.ReferenceFrequency() * ratios[semitones];
        for (; octaves > 0; --octaves) {
            if (frequency > FLT_MAX / 2.0f) {
                return 0.0f;
            }
            frequency *= 2.0f;
        }
        for (; octaves < 0; ++octaves) {
            frequency *= 0.5f;
        }
        return frequency;
    }

    friend constexpr bool operator==(EqualTemperament a, EqualTemperament b) noexcept {
        return a._tuning == b._tuning;
    }
 
    friend constexpr bool operator!=(EqualTemperament a, EqualTemperament b) noexcept {
        return !(a == b);
    }
};
 
} // namespace MCC
 
#endif // MCC_TUNING_EQUAL_TEMPERAMENT_H