zap_hashbits
int zap_hashbits(zap_t *zap);
if (zap_f_phys(zap)->zap_ptrtbl.zt_shift >= zap_hashbits(zap) - 2)
h &= ~((1ULL << (64 - zap_hashbits(zap))) - 1);
return ((zc->zc_hash >> (64 - zap_hashbits(zc->zc_zap))) |
((uint64_t)zc->zc_cd << zap_hashbits(zc->zc_zap)));
hb = zap_hashbits(zc->zc_zap);