TptSvf.h

// DSPark - Professional Audio DSP Framework
// Copyright (c) 2026 Cristian Moresi - MIT License
 
#pragma once
 
#include "../DspMath.h"
 
namespace dspark::detail
{
template <FloatType T> struct TptSvfState
{
    T ic1eq = T(0);
    T ic2eq = T(0);
};
 
template <FloatType T> struct TptSvfOutput
{
    T lowpass;
    T bandpass;
};
 
template <FloatType T>
[[nodiscard]] inline TptSvfOutput<T> tptSvfStep(T input, TptSvfState<T> &state, T a1, T a2,
                                                T a3) noexcept
{
    const T v3 = input - state.ic2eq;
    const T v1 = a1 * state.ic1eq + a2 * v3;
    const T v2 = state.ic2eq + a2 * state.ic1eq + a3 * v3;
    state.ic1eq = T(2) * v1 - state.ic1eq;
    state.ic2eq = T(2) * v2 - state.ic2eq;
    return {v2, v1};
}
} // namespace dspark::detail