Example:

C:\gfortran\clf\negative_boz>type negative_boz.f90
program negative_boz
use ISO_C_BINDING
integer, parameter :: bk8 = selected_int_kind(2)
integer, parameter :: bk16 = selected_int_kind(4)
integer, parameter :: bk32 = selected_int_kind(9)
integer, parameter :: bk64 = selected_int_kind(18)
integer, parameter :: bk128 = selected_int_kind(36)
integer(bk8) i8
integer(bk16) i16
integer(bk32) i32
integer(bk64) i64
integer(bk128) i128