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Write two functions log2d and log2u, which calculate the binary logarithm of their argument n rounded down and up, respectively. n is assumed to be positive. Print the result of these functions for numbers from 1 to 12.
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program main
  implicit none
  integer :: i
  do i=1,12
     print *,i,log2d(i),log2u(i)
  end do
contains
  integer function log2d (n)
    integer, intent(in) :: n
    log2d = bit_size(n) - 1 - leadz(n)
  end function log2d

  integer function log2u (n)
    integer, intent(in) :: n
    log2u = bit_size(n) - leadz(n-1)
  end function log2u
end program main