! ******************************************************************
! ******************************************************************

function drand(ix)

  implicit none

  ! This is the random number generator of Schrage:
  !
  ! L. Schrage, A more portable Fortran random number generator, ACM
  ! Transactions on Mathematical Software 5 (1979), 132-138.

  ! FUNCTION TYPE
  real(kind=8) :: drand

  ! SCALAR ARGUMENT
  real(kind=8), intent(inout) :: ix

  ! LOCAL ARRAYS
  real(kind=8) :: a,p,b15,b16,xhi,xalo,leftlo,fhi,k

  data a/16807.d0/,b15/32768.d0/,b16/65536.d0/,p/2147483647.d0/

  xhi= ix/b16
  xhi= xhi - dmod(xhi,1.d0)
  xalo= (ix-xhi*b16)*a
  leftlo= xalo/b16
  leftlo= leftlo - dmod(leftlo,1.d0)
  fhi= xhi*a + leftlo
  k= fhi/b15
  k= k - dmod(k,1.d0)
  ix= (((xalo-leftlo*b16)-p)+(fhi-k*b15)*b16)+k
  if (ix.lt.0) ix= ix + p
  drand= ix*4.656612875d-10

  return

end function drand