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/// @file	LowPassFilter.h
/// @brief	A class to implement a second order low pass filter 
/// Author: Leonard Hall <LeonardTHall@gmail.com>
/// Adapted for PX4 by Andrew Tridgell

#pragma once

namespace math
{
class __EXPORT LowPassFilter2p
{
public:
    // constructor
    LowPassFilter2p(float sample_freq, float cutoff_freq) {
        // set initial parameters
        set_cutoff_frequency(sample_freq, cutoff_freq);
        _delay_element_1 = _delay_element_2 = 0;
    }

    // change parameters
    void set_cutoff_frequency(float sample_freq, float cutoff_freq);

    // apply - Add a new raw value to the filter 
    // and retrieve the filtered result
    float apply(float sample);

    // return the cutoff frequency
    float get_cutoff_freq(void) const {
        return _cutoff_freq;
    }

private:
    float           _cutoff_freq; 
    float           _a1;
    float           _a2;
    float           _b0;
    float           _b1;
    float           _b2;
    float           _delay_element_1;        // buffered sample -1
    float           _delay_element_2;        // buffered sample -2
};

} // namespace math