# Bug? (large integers...) **URL:** \ **Category:** Uncategorized\ **Created:** [December 31, 2023, 9:14pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086 "2023-12-31T21:14:37Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![TIMOTHY989](https://avatars.discourse-cdn.com/v4/letter/t/a9adbd/32.png) [@TIMOTHY989](https://fortran-lang.discourse.group/u/TIMOTHY989)\ **Post date:** [December 31, 2023, 9:14pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/1 "2023-12-31T21:14:37Z")
integer :: x ``` x = (2*33333333333333333) print *, x ``` end program Calculated a (large) negative value (!) yet use 1 less “3” or one more “3” returns large positive integer…(?) ---
**Author:** ![DavidB](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@DavidB](https://fortran-lang.discourse.group/u/DavidB)\ **Post date:** [December 31, 2023, 9:34pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/2 "2023-12-31T21:34:13Z")
Not a bug. See [Integer overflow](https://en.wikipedia.org/wiki/Integer_overflow). Fortran integers are signed integers. On most systems the default integer is 32-bit. The maximum value of a 32-bit signed integer is 2147483647. You can see this with a simpler example. ```auto $ cat overflow.f90 integer :: x x = 33333333333333333 write(*,*) x end $ gfortran -o overflow.exe -Wall overflow.f90 overflow.f90:2:23: 2 | x = 33333333333333333 | 1 Error: Integer too big for its kind at (1). This check can be disabled with the option ‘-fno-range-check’ $ gfortran -o overflow.exe -Wall -fno-range-check overflow.f90 $ ./overflow.exe 1954764117 ``` You need to use an integer of a kind with sufficient range to store your values. Something like ```auto $ cat nooverflow.f90 integer, parameter :: k = selected_int_kind(20) integer(kind=k) :: x x = 33333333333333333_k write(*,*) x end $ gfortran -o nooverflow.exe -Wall nooverflow.f90 $ ./nooverflow.exe 33333333333333333 ``` ---
**Author:** ![rbitr](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rbitr](https://fortran-lang.discourse.group/u/rbitr)\ **Post date:** [December 31, 2023, 9:38pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/3 "2023-12-31T21:38:17Z")
Edit: I got beat to the answer. I’ll leave mine because I’m still curious about the error I have. Edit 2: I see from the example above I need to do `z = (2*33333333333333333_wp)` which removes the error. In principle I think you should use [SELECTED\_INT\_KIND (The GNU Fortran Compiler)](https://gcc.gnu.org/onlinedocs/gfortran/SELECTED_005fINT_005fKIND.html) to ensure the integer is big enough to hold the value. ```auto program ex1 integer :: x integer(8) :: y integer,parameter :: wp = selected_int_kind(17) integer(kind=wp) :: z x = (2*33333333333333333) y = (2*33333333333333333) z = (2*33333333333333333) print *, wp print *, x, y, z end program ``` ```auto % gfortran ex1.f90 -fno-range-check -o ex % ./ex 8 -385439062 66666666666666666 66666666666666666 ``` An 8-byte int is required… curiously, if I compile without the `-fno-range-check` I get an error for all three assignments. ```auto % gfortran ex1.f90 -o ex ex1.f90:8:25: 8 | x = (2*33333333333333333) | 1 Error: Integer too big for its kind at (1). This check can be disabled with the option ‘-fno-range-check’ ex1.f90:9:25: 9 | y = (2*33333333333333333) | 1 Error: Integer too big for its kind at (1). This check can be disabled with the option ‘-fno-range-check’ ex1.f90:10:25: 10 | z = (2*33333333333333333) | 1 Error: Integer too big for its kind at (1). This check can be disabled with the option ‘-fno-range-check’ ``` See also [Doctor Fortran in "It Takes All KINDs" - Doctor Fortran](https://stevelionel.com/drfortran/2017/03/27/doctor-fortran-in-it-takes-all-kinds/) ---
**Author:** ![davidpfister](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/davidpfister/32/3949_2.png) [@davidpfister](https://fortran-lang.discourse.group/u/davidpfister)\ **Post date:** [December 31, 2023, 9:57pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/4 "2023-12-31T21:57:21Z")
Now if you really need to deal with huge integers there are few libraries for it - [fmlib](http://dmsmith.lmu.build/) - [Pcalcfun](https://web.archive.org/web/20230606063617/http://jean-pierre.moreau.pagesperso-orange.fr/Fortran/pcalcfun_f90.txt) ---
**Author:** ![DavidB](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@DavidB](https://fortran-lang.discourse.group/u/DavidB)\ **Post date:** [December 31, 2023, 10:02pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/5 "2023-12-31T22:02:03Z")
Undecorated integer constants have default kind, so 33333333333333333 overflows. You need to use 33333333333333333\_wp. Same with floating point constants. Common mistake. ---
**Author:** ![TIMOTHY989](https://avatars.discourse-cdn.com/v4/letter/t/a9adbd/32.png) [@TIMOTHY989](https://fortran-lang.discourse.group/u/TIMOTHY989)\ **Post date:** [December 31, 2023, 10:03pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/6 "2023-12-31T22:03:36Z")
Thanks for the clarification! (Ah, ok) yep- it’s been a wee while …FORTRAN 77 , back in 1984 ( ! ) on an ICL mainframe Glad 2 see this proj & love the Mandelbrot , BTW all the best Tim ---
**Author:** ![TIMOTHY989](https://avatars.discourse-cdn.com/v4/letter/t/a9adbd/32.png) [@TIMOTHY989](https://fortran-lang.discourse.group/u/TIMOTHY989)\ **Post date:** [December 31, 2023, 10:04pm UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/7 "2023-12-31T22:04:33Z")
Thanx! 😀👍 ---
**Author:** ![JohnCampbell](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@JohnCampbell](https://fortran-lang.discourse.group/u/JohnCampbell)\ **Post date:** [January 1, 2024, 6:45am UTC](https://fortran-lang.discourse.group/t/bug-large-integers/7086/8 "2024-01-01T06:45:28Z")
It is interesting that with gfortran -fno-range-check, 4-byte integer constants are promoted to 8-byte. The following adaptation removes the requirement for “-fno-range-check”, while still allowing integer overflow for calculating x ```auto program ex1 integer,parameter :: wp = selected_int_kind(17) integer :: x integer(8) :: y integer(kind=wp) :: z integer(wp) :: t = 33333333333333333_wp y = (2*33333333333333333_wp) z = (2*t) ! x = (2*33333333333333333_wp) x = y print *, wp print *, x, y, z, t end program ``` I have always objected to Fortran compilers not being allowed to correctly interpret the integer constant 33333333333333333, which would be read correctly from an input file.