Fortran Integer Range

[arango]

• Recently, I introduced at resetting of the reporting of the time-step counter in routine diag.F after 10 billion steps. The formatted field is I10 (ten digits):

             WRITE (stdout,30) MOD(iic(ng)-1,10000000000),               &
             ....
          30 FORMAT (i10, ....
  

  Some compilers seem to have issue with this integer operation. For example gfortran gives:

  diag.f90:383:53:
  
             WRITE (stdout,30) MOD(iic(ng),10000000000),                 &
                                                     1
  Error: Integer too big for its kind at (1). This check can be disabled with the option -fno-range-check
  

To avoid issues with different compilers, I am changing the statement to a floating-point operation:

           WRITE (stdout,30) INT(MOD(REAL(iic(ng)-1,r8),1.0E+10_r8)),  &
           ...

It is more robust to use the MOD intrinsic function with floating-point values.

• Cleaned the documentation in mod_kinds.F. Both byte and bit were used and it is better to do it in bits. Notice that byte and bit are not the same and can get confusing.

• I renamed the i4b integer kind to i8b in module ran_state.F to agree with the 32-bit documentation of the random numbers and the definition in mod_kinds.F.

---

Be aware that SELECTED_INT_KIND and KIND are different in Fortran when declaring integers:

     integer, parameter :: i8b = selected_int_kind(8)

     integer          :: i                    ! default
     integer (i8b)    :: i8
     integer (KIND=8) :: j8

A simple program can be written to examine the largest integer possible using the HUGE intrinsic function:

                Default, HUGE(i  ) =   2147483647
  SELECTED_INT_KIND(1 ), HUGE(i1 ) =   127
  SELECTED_INT_KIND(2 ), HUGE(i2 ) =   127
  SELECTED_INT_KIND(4 ), HUGE(i4 ) =   32767
  SELECTED_INT_KIND(8 ), HUGE(i8 ) =   2147483647
  SELECTED_INT_KIND(9 ), HUGE(i9 ) =   2147483647
  SELECTED_INT_KIND(16), HUGE(i16) =   9223372036854775807

               KIND(1 ), HUGE(j1 ) =   127
               KIND(2 ), HUGE(j2 ) =   32767
               KIND(4 ), HUGE(j4 ) =   2147483647
               KIND(8 ), HUGE(j8 ) =   9223372036854775807

Notice that the SELECTED_iNT_KIND(8) and KIND=8 have very different values. Also notice that the default declaration have the same values as SELECTED_iNT_KIND(8) or KIND=8.