MULT_HIGH (integer*8, integer*8)

  Class:  Elemental function - Specific

  A function that multiplies two 64-bit unsigned integers.  The
  result is of type INTEGER*8.  The result value is the upper
  (leftmost) 64 bits of the 128-bit unsigned result.

  This function cannot be passed as an actual argument.

  Consider the following:

          INTEGER(8) I,J,K
          I=2_8**53
          J=2_8**51
          K = MULT_HIGH (I,J)
          PRINT *,I,J,K
          WRITE (6,1000)I,J,K
  1000    FORMAT (' ', 3(Z,1X))
          END

  This example prints the following:

    9007199254740992      2251799813685248         1099511627776
        20000000000000           8000000000000             10000000000