src/synth.c


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#include <stdlib.h>
#include <math.h>
#include <errno.h>

#include <xas/synth.h>

static int16_t sample_sine(xas_synth *synth) {
    int16_t ret;
    static float tau = 2.0f * M_PI;

    if (synth->state == XAS_SYNTH_ACTIVE) {
        ret = (int16_t)roundf(synth->gain * (INT16_MAX >> 2) * sinf(synth->phase));

        synth->phase += tau / (synth->format.sample_rate / synth->frequency);

        if (synth->phase > tau) {
            synth->phase -= tau;
        }
    } else {
        ret = 0;
    }

    return ret;
}

static int16_t sample_square(xas_synth *synth) {
    int16_t ret;
    static float tau = 2.0f * M_PI;

    float duty = synth->duty;

    if (synth->state == XAS_SYNTH_ACTIVE) {
        ret = (synth->phase - (duty * tau)) > 0.0?
            (int16_t)roundf(synth->gain * (INT16_MAX / 4)):
            (int16_t)roundf(synth->gain * (INT16_MIN / 4));

        synth->phase += tau / (synth->format.sample_rate / synth->frequency);

        if (synth->phase > tau) {
            synth->phase -= tau;
        }
    } else {
        ret = 0;
    }

    return ret;
}

static int16_t sample_triangle(xas_synth *synth) {
    int16_t ret;
    static float tau = 2.0f * M_PI;

    if (synth->state == XAS_SYNTH_ACTIVE) {
        float v = 2.0f * fabs(2.0f * fabs(synth->phase - floorf(synth->phase + 0.5))) - 1.0f;

        ret = (int16_t)roundf(synth->gain * (INT16_MAX >> 2) * v);

        synth->phase += tau / (synth->format.sample_rate / synth->frequency);

        if (synth->phase > tau) {
            synth->phase -= tau;
        }
    } else {
        ret = 0;
    }

    return ret;
}

static int16_t sample_sawtooth(xas_synth *synth) {
    int16_t ret;
    static float tau = 2.0f * M_PI;

    if (synth->state == XAS_SYNTH_ACTIVE) {
        float v = 2.0f * (synth->phase / tau - 0.5f);

        ret = (int16_t)roundf(synth->gain * (INT16_MAX >> 2) * v);

        synth->phase += tau / (synth->format.sample_rate / synth->frequency);

        if (synth->phase > tau) {
            synth->phase -= tau;
        }
    } else {
        ret = 0;
    }

    return ret;
}

static ssize_t synth_fill(xas_synth *synth,
                          int16_t *samples,
                          size_t count,
                          xas_audio_stream *stream) {
    size_t i;

    for (i=0; i<count; i++) {
        samples[i] = synth->sample(synth);
    }

    return count;
}

static int synth_start(xas_synth *synth) {
    xas_synth_start(synth);

    return 0;
}

static int synth_stop(xas_synth *synth) {
    xas_synth_stop(synth);

    return 0;
}

static int set_gain(xas_synth *synth, float gain) {
    xas_synth_set_gain(synth, gain);

    return 0;
}

static int set_type(xas_synth *synth, enum xas_synth_type type) {
    switch (type) {
        case XAS_SYNTH_SINE:     synth->sample = sample_sine;     break;
        case XAS_SYNTH_SQUARE:   synth->sample = sample_square;   break;
        case XAS_SYNTH_TRIANGLE: synth->sample = sample_triangle; break;
        case XAS_SYNTH_SAWTOOTH: synth->sample = sample_sawtooth; break;

        default:
            errno = EINVAL;

            goto error_invalid_type;
    }

    synth->type = type;

    return 0;

error_invalid_type:
    return -1;
}

xas_synth *xas_synth_new(xas_audio_format format,
                             size_t buffer_size,
                             enum xas_synth_type type) {
    xas_synth *synth;

    if ((synth = malloc(sizeof(*synth))) == NULL) {
        goto error_malloc_synth;
    }

    synth->obj.start      = (xas_object_start_callback)synth_start;
    synth->obj.stop       = (xas_object_stop_callback)synth_stop;
    synth->obj.set_gain   = (xas_object_set_gain_callback)set_gain;
    synth->obj.stream_new = (xas_object_stream_new_callback)xas_synth_stream_new;
    synth->obj.destroy    = (xas_object_destroy_callback)xas_synth_destroy;

    synth->state     = XAS_SYNTH_IDLE;
    synth->phase     = 0.0f;
    synth->gain      = XAS_SYNTH_DEFAULT_GAIN;
    synth->duty      = XAS_SYNTH_DEFAULT_DUTY;
    synth->frequency = XAS_SYNTH_DEFAULT_FREQUENCY;

    synth->format.channels    = XAS_AUDIO_MONO;
    synth->format.sample_size = format.sample_size;
    synth->format.sample_rate = format.sample_rate;
    synth->buffer_size        = buffer_size;

    if (set_type(synth, type) < 0) {
        goto error_set_type;
    }

    return synth;

error_set_type:
    free(synth);

error_malloc_synth:
    return NULL;
}

void xas_synth_destroy(xas_synth *synth) {
    free(synth);
}

void xas_synth_set_gain(xas_synth *synth, float gain) {
    synth->gain = gain;
}

void xas_synth_set_duty(xas_synth *synth, float duty) {
    synth->duty = duty;
}

void xas_synth_set_type(xas_synth *synth, enum xas_synth_type type) {
    set_type(synth, type);
}

void xas_synth_set_frequency(xas_synth *synth, size_t frequency) {
    synth->frequency = frequency;
}

void xas_synth_start(xas_synth *synth) {
    synth->state = XAS_SYNTH_ACTIVE;
}

void xas_synth_stop(xas_synth *synth) {
    synth->state = XAS_SYNTH_IDLE;
    synth->phase = 0.0f;
}

xas_audio_stream *xas_synth_stream_new(xas_synth *synth) {
    return xas_audio_stream_new_source((xas_audio_fill)synth_fill,
                                          NULL,
                                          synth->format,
                                          synth->buffer_size,
                                          synth);
}