oscillator.c

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/*
 * © Stuart Longland VK4MSL
 * SPDX-License-Identifier: MIT
 */
 
#include <assert.h>
#include <libsstvenc/oscillator.h>
#include <math.h>
#include <stdint.h>
 
#define SSTVENC_OSC_PHASE_FRAC_BITS (29)
 
#define SSTVENC_OSC_PHASE_FRAC_SCALE                                         \
        ((double)(1 << SSTVENC_OSC_PHASE_FRAC_BITS))
 
double sstvenc_osc_get_frequency(const struct sstvenc_oscillator* const osc) {
        return ((double)(((uint64_t)osc->phase_inc) * osc->sample_rate))
               / (2 * M_PI * SSTVENC_OSC_PHASE_FRAC_SCALE);
}
 
void sstvenc_osc_set_frequency(struct sstvenc_oscillator* const osc,
                               double                           frequency) {
        assert(frequency >= 0);
        assert(frequency < (osc->sample_rate / 2));
 
        osc->phase_inc = (2 * M_PI * frequency * SSTVENC_OSC_PHASE_FRAC_SCALE)
                         / osc->sample_rate;
}
 
void sstvenc_osc_init(struct sstvenc_oscillator* const osc, double amplitude,
                      double frequency, double offset, uint32_t sample_rate) {
        osc->amplitude   = amplitude;
        osc->offset      = offset;
        osc->output      = 0.0;
        osc->sample_rate = sample_rate;
        osc->phase       = 0;
        sstvenc_osc_set_frequency(osc, frequency);
}
 
void sstvenc_osc_compute(struct sstvenc_oscillator* const osc) {
        if (osc->sample_rate) {
                /* Compute output */
                osc->output = osc->amplitude
                              * sin(osc->offset
                                    + (((double)osc->phase)
                                       / SSTVENC_OSC_PHASE_FRAC_SCALE));
 
                /* Increment phase, modulo 2Pi */
                osc->phase += osc->phase_inc;
                osc->phase
                    %= (uint32_t)(2 * M_PI * SSTVENC_OSC_PHASE_FRAC_SCALE);
        }
}