void bigint_add3(word z[], const word x[], size_t x_size,
                           const word y[], size_t y_size)
   {
   z[(x_size > y_size ? x_size : y_size)] +=
      bigint_add3_nc(z, x, x_size, y, y_size);
   }
void bigint_add3(word z[], const word x[], size_t x_size,
                           const word y[], size_t y_size)
   {
   z[(x_size > y_size ? x_size : y_size)] +=
      bigint_add3_nc(z, x, x_size, y, y_size);
   }