MOS calculation

static int internal_get_and_notify_call_statistics(pjsua_call_id call_id, long comm_id)
{
    pj_status_t status = PJ_SUCCESS;
    pjsua_stream_stat stat;
    int LOCAL_DELAY = 30;
    float R;
    float a = 0.0f; //iLBC a = 10;
    float b = 19.8f;
    float c = 29.7f;
    int rx_pkts = 0;
    int tx_pkts = 0;
    float rx_loss = 0.0;
    float tx_loss = 0.0;
    float rx_jit = 0.0;
    float tx_jit = 0.0;
    float avg_rtt = 0.0;
    float avg_latency = 0.0;
    float MOS = 0.0;

    if (internal_call_has_media(call_id)) {
        PJ_LOG(4, (THIS_FILE,"Call have had media. Calculate the statistics."));
    } else {
        PJ_LOG(4, (THIS_FILE,"Call has never established media, return with no calculations."));
        return PJ_EINVAL;
    }
    status = pjsua_call_get_stream_stat(call_id, 0, &stat);

    //Only calculate the MOS if we have sent and received packets (also protects us from potential division by zero).
    if (status == PJ_SUCCESS) {
        PJ_LOG(4, (THIS_FILE,
                   "pjsip stats: stat.rtcp.rx.pkt=%d : stat.rtcp.tx.pkt=%d : stat.rtcp.rx.loss=%d : stat.rtcp.rtt.mean=%d : stat.rtcp.rx.dup=%d ",
                   stat.rtcp.rx.pkt, stat.rtcp.tx.pkt, stat.rtcp.rx.loss, stat.rtcp.rtt.mean, stat.rtcp.rx.dup));
        rx_pkts = stat.rtcp.rx.pkt;
        tx_pkts = stat.rtcp.tx.pkt;
        rx_loss = (stat.rtcp.rx.pkt == 0) ? 1.0f : ((float)stat.rtcp.rx.loss) / (float)((stat.rtcp.rx.pkt + stat.rtcp.rx.loss));
        tx_loss = (stat.rtcp.tx.pkt == 0) ? 1.0f : ((float)stat.rtcp.tx.loss) / (float)stat.rtcp.tx.pkt;
        rx_jit = (float)stat.rtcp.rx.jitter.mean/1000;
        tx_jit = (float)stat.rtcp.tx.jitter.mean/1000;
        avg_rtt = stat.rtcp.rtt.mean / 2000.0f;
        if (avg_rtt == 0) { //means that there is no rtt information in rtcp packets so we estimate value
            PJ_LOG(4, (THIS_FILE, "There is no avg_rtt in rtcp packet. We set avg_rtt to estimated fixed value"));
            avg_rtt = TU_AVERAGE_RTT_ESTIMATION;
        }
        //Johan: For the local delay we also have to take sound card latency and jbuf state into account.
        avg_latency = (stat.rtcp.rtt.mean / 2000.0f) + LOCAL_DELAY + pjsua_var.media_cfg.snd_play_latency +
                      pjsua_var.media_cfg.snd_rec_latency + rx_jit;

        //Calculate R
        {
            float d = avg_latency;
            float d2 = d-177.3f;
            float Id = 0.024f * d + 0.11f * (d - 177.3f) * (d2 < 0 ? 0 : 1);
            float P = rx_loss; //stats.getPacketLoss();
            float Ie = a + b * (float)log(1 + c * P);
            R = 94.2f - Id - Ie;
            PJ_LOG(4, (THIS_FILE, "d=%f : d2=%f : Id=%f : P=%f : Ie=%f : R=%f", d, d2, Id, P, Ie, R));
        }

        if (R < 0) {
            MOS = 1;
        } else if (R > 100) {
            MOS = 4.5;
        } else {
            MOS = 1 + 0.035f * R + 7.10f/1000000 * R * (R - 60) * (100 - R);
        }
        PJ_LOG(4, (THIS_FILE,
                   "Our stats: rx_pkts=%d tx_pkts=%d rx_loss=%f \naverage rtt=%f average_latency=%f R=%f  \nMOS score : %3.1f \n", rx_pkts,
                   tx_pkts, rx_loss, avg_rtt, avg_latency, R, MOS));
        //notifying statistics
        tu_var.cfg.callbacks.on_call_media_statistics(get_call_uuid(call_id), comm_id, rx_pkts, tx_pkts, rx_loss, tx_loss,
                rx_jit, tx_jit, avg_rtt, avg_latency, MOS);
    } else {

        PJ_LOG(1, (THIS_FILE, "Failed to call pjsua_call_get_stream_stat, status=%d",status));
    }
    return status;
}