Forward QMF

qmf_forward.c

void forward_qmf(float *out_low, float *out_high, float *delay, const float *in,
                 int samples, int delay_samples)
{
    memcpy(delay, delay + samples, delay_samples * sizeof(float));
    memcpy(delay + delay_samples, in, samples * sizeof(float));

    for (int i = 0; i < samples; i += 2) {
        float low = 0.0f, high = 0.0f;

        /* Can be done via float_dsp */
        for (int j = 0; j < (delay_samples + 2); j += 2) {
            low  += qmf_window[j + 0] * in[i - j + 47];
            high += qmf_window[j + 1] * in[i - j + 46];
        }

        out_low [i >> 1] = low + high;
        out_high[i >> 1] = low - high;
    }
}