Ead.h

/*
 * Ead.h
 *
 * Adapted from ead~.c puredata external (creb library)
 *
 * This file is part of Mozzi.
 *
 * Copyright (c) 2000-2003 by Tom Schouten
 * Copyright 2012 Tim Barrass
 * Copyright 2012-2024 Tim Barrass and the Mozzi Team
 *
 * Mozzi is licensed under the GNU Lesser General Public Licence (LGPL) Version 2.1 or later.
 *
 */
 
#ifndef EAD_H_
#define EAD_H_
 
#include "math.h"
#include "mozzi_fixmath.h"
 
 
class Ead
{
 
public:
 
    Ead(unsigned int update_rate) : UPDATE_RATE(update_rate)
    {
        ;
    }
 
    inline
    void setAttack(unsigned int attack_ms)
    {
        Q8n8attack = float_to_Q8n8(millisToOneMinusRealPole(attack_ms));
    }
 
 
    inline
    void setDecay(unsigned int decay_ms)
    {
        Q8n8decay = float_to_Q8n8(millisToOneMinusRealPole(decay_ms));
    }
 
 
    inline
    void set(unsigned int attack_ms, unsigned int decay_ms)
    {
        setAttack(attack_ms);
        setDecay(decay_ms);
    }
 
 
    inline
    void start()
    {
        Q8n24state = 0;
        attack_phase = true;
    }
 
 
    inline
    void start(unsigned int attack_ms, unsigned int decay_ms)
    {
        set(attack_ms, decay_ms);
        //Q8n24state = 0; // don't restart from 0, just go from whatever the current level is, to avoid glitches
        attack_phase = true;
    }
 
 
    inline
    uint8_t next()
    {
        if(attack_phase)
        {
            // multiply A(a1,b1) * A(a2,b2) = A(a1+a2, b1+b2)
            Q8n24state += (((Q8n24)(Q8n24_FIX1 - Q8n24state) * Q8n8attack)) >> 8; // Q8n24, shifts all back into n24
            if (Q8n24state >= Q8n24_FIX1-256)
            {
                Q8n24state = Q8n24_FIX1-256;
                attack_phase = false;
            }
        }else{ /* decay phase */
            Q8n24state -= (Q8n24state * Q8n8decay)>>8;
        }
        return Q8n24_to_Q0n8(Q8n24state);
    }
 
 
private:
 
    Q8n8 Q8n8attack;
    Q8n8 Q8n8decay;
    Q8n24 Q8n24state;
    bool attack_phase;
    const unsigned int UPDATE_RATE;
 
 
    /* convert milliseconds to 1-p, with p a real pole */
    inline
    float millisToOneMinusRealPole(unsigned int milliseconds)
    {
        static const float NUMERATOR = 1000.0f * log(0.001f);
        return  -expm1(NUMERATOR / ((float)UPDATE_RATE * milliseconds));
    }
 
 
    // Compute exp(x) - 1 without loss of precision for small values of x.
    inline
    float expm1(float x)
    {
        if (fabs(x) < 1e-5)
        {
            return x + 0.5*x*x;
        }
        else
        {
            return exp(x) - 1.0;
        }
    }
 
};
 
#endif /* EAD_H_ */