Question

Currently I’m brushing up on my Fortran95 knowledge (don’t ask why)…

I’m running in to a problem though. How does one handle large integers, eg. the size of: ~700000000000

INTEGER(KIND=3) cannot hold this number.
If anyone is interested the compiler I have available is Silverfrost FTN95.

I am using the integer to run through a larger set of data.

Do you have any suggestions?

Answer 1

The standard solution (since Fortran 95, so I assume your compiler supports it) is to use the SELECTED_INT_KIND intrinsic to probe for valid integer kinds (whose values are compiler dependent) and the HUGE intrinsic.

• SELECTED_INT_KIND (R) returns the kind type parameter of an integer type that represents all integer values n with −10^R < n < 10^R (and returns -1 if no such type exist).
• HUGE (K) returns the largest representable number in integer type of kind K.

For example, on my Mac with an x86_64 processor (gfortran compiler, 64-bit mode), the following program:

  print *, selected_int_kind(1)
  print *, selected_int_kind(4)
  print *, selected_int_kind(8)
  print *, selected_int_kind(16)
  print *, selected_int_kind(32)
  print *, selected_int_kind(64)
  print *, huge(0_1)
  print *, huge(0_2)
  print *, huge(0_4)
  print *, huge(0_8)
  print *, huge(0_16)
  end

outputs:

           1
           2
           4
           8
          16
          -1
  127
  32767
  2147483647
  9223372036854775807
 170141183460469231731687303715884105727

which tells me that I’d use an integer(kind=8) for your job.