MPN_SQR_N_RECURSE
MPN_SQR_N_RECURSE(prodp, up, esize, tspace);
MPN_SQR_N_RECURSE(prodp + size, up + hsize, hsize, tspace);
MPN_SQR_N_RECURSE(tspace, prodp, hsize, tspace + size);
MPN_SQR_N_RECURSE(tspace, up, hsize, tspace + size);