static int sbr_hf_calc_npatches(AACContext *ac, SpectralBandReplication *sbr)
{
    int i, k, sb = 0;
    int msb = sbr->k[0];
    int usb = sbr->kx[1];
    int goal_sb = ((1000 << 11) + (sbr->sample_rate >> 1)) / sbr->sample_rate;

    sbr->num_patches = 0;

    if (goal_sb < sbr->kx[1] + sbr->m[1]) {
        for (k = 0; sbr->f_master[k] < goal_sb; k++) ;
    } else
        k = sbr->n_master;

    do {
        int odd = 0;
        for (i = k; i == k || sb > (sbr->k[0] - 1 + msb - odd); i--) {
            sb = sbr->f_master[i];
            odd = (sb + sbr->k[0]) & 1;
        }

        // Requirements (14496-3 sp04 p205) sets the maximum number of patches to 5.
        // After this check the final number of patches can still be six which is
        // illegal however the Coding Technologies decoder check stream has a final
        // count of 6 patches
        if (sbr->num_patches > 5) {
            av_log(ac->avccontext, AV_LOG_ERROR, "Too many patches: %d\n", sbr->num_patches);
            return -1;
        }

        sbr->patch_num_subbands[sbr->num_patches]  = FFMAX(sb - usb, 0);
        sbr->patch_start_subband[sbr->num_patches] = sbr->k[0] - odd - sbr->patch_num_subbands[sbr->num_patches];

        if (sbr->patch_num_subbands[sbr->num_patches] > 0) {
            usb = sb;
            msb = sb;
            sbr->num_patches++;
        } else
            msb = sbr->kx[1];

        if (sbr->f_master[k] - sb < 3)
            k = sbr->n_master;
    } while (sb != sbr->kx[1] + sbr->m[1]);

    if (sbr->patch_num_subbands[sbr->num_patches-1] < 3 && sbr->num_patches > 1)
        sbr->num_patches--;

    return 0;
}