crossfade.hpp

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#pragma once

 
#include <cmath>
 
namespace pulp::signal {

enum class CrossfadeGainLaw {
    EqualGain,   
    EqualPower,  
};

template <typename T>
constexpr T crossfade_smoothstep(T t) noexcept {
    if (t < T{0}) t = T{0};
    else if (t > T{1}) t = T{1};
    return t * t * (T{3} - T{2} * t);
}

template <typename T>
inline void crossfade_gains(T u, CrossfadeGainLaw law,
                            T& old_gain, T& new_gain) noexcept {
    if (law == CrossfadeGainLaw::EqualPower) {
        // π/2 to full double precision; `u * kHalfPi` reproduces the callers'
        // `u * 0.5 * π` (u·0.5 is exact, so the single rounding is identical).
        constexpr T kHalfPi = T{1.57079632679489661923};
        const T theta = u * kHalfPi;
        old_gain = std::cos(theta);
        new_gain = std::sin(theta);
    } else {
        old_gain = T{1} - u;
        new_gain = u;
    }
}
 
}  // namespace pulp::signal