fm95/lib/oscillator.c

#include "oscillator.h"

void init_oscillator(Oscillator *osc, float frequency, float sample_rate) {
	osc->phase = 0.0f;
	osc->phase_increment = (M_2PI * frequency) / sample_rate;
	osc->sample_rate = sample_rate;
}

inline void change_oscillator_frequency(Oscillator *osc, float frequency) {
	osc->phase_increment = (M_2PI * frequency) / osc->sample_rate;
}

float get_oscillator_sin_sample(Oscillator *osc) {
	float sample = sinf(osc->phase);
	advance_oscillator(osc);
	return sample;
}

float get_oscillator_cos_sample(Oscillator *osc) {
	float sample = cosf(osc->phase);
	advance_oscillator(osc);
	return sample;
}

float get_oscillator_sin_multiplier_ni(Oscillator *osc, float multiplier) {
	return sinf(osc->phase * multiplier);
}

float get_oscillator_cos_multiplier_ni(Oscillator *osc, float multiplier) {
	return cosf(osc->phase * multiplier);
}

inline bool advance_oscillator(Oscillator *osc) {
	osc->phase += osc->phase_increment;
	if (osc->phase >= M_2PI) {
		osc->phase -= M_2PI;
		return true;
	} return false;
}

bool oscillator_did_cycle(Oscillator *osc, float phase_shift, float *prev_shifted_phase) {
    float shifted = osc->phase + phase_shift;

    // wrap into [0, 2π)
    while (shifted >= M_2PI) shifted -= M_2PI;
    while (shifted < 0.0f)   shifted += M_2PI;

    bool crossed = shifted < *prev_shifted_phase;
    *prev_shifted_phase = shifted;
    return crossed;
}