docs: def _ints_arr_to_bits(ints_arr, out):
      """
      Convert an array of integers representing the set bits into the
      corresponding integer.
  
      Compiled as a ufunc by Numba's `@guvectorize`: if the input is a
      2-dim array with shape[0]=K, the function returns a 1-dim array of
      K converted integers.
  
      Parameters
      ----------
      ints_arr : ndarray(int32, ndim=1)
          Array of distinct integers from 0, ..., 63.
  
      Returns
      -------
      np.uint64
          Integer with set bits represented by the input integers.
  
      Examples
      --------
      >>> ints_arr = np.array([0, 1, 2], dtype=np.int32)
      >>> _ints_arr_to_bits(ints_arr)
      7
      >>> ints_arr2d = np.array([[0, 1, 2], [3, 0, 1]], dtype=np.int32)
      >>> _ints_arr_to_bits(ints_arr2d)
      array([ 7, 11], dtype=uint64)
  
      """
      m = ints_arr.shape[0]
      out[0] = 0
      for i in range(m):
          out[0] |= np.uint64(1) << np.uint64(ints_arr[i])