https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99561
--- Comment #2 from kargl at gcc dot gnu.org --- (In reply to kargl from comment #1) > (In reply to Michal Paszta from comment #0) > > In this line of code: > > > > INTEGER(KIND=1) :: var8 = 257_2 > > > > we try to cast an integer of kind 2 (16 bits) onto an integer of kind 1 (8 > > bits, value up to 256). This will result in a truncation of the value and is > > allowed by the Fortran 2018 Standard, see Table 10.9, Fortran 2018 Standard. > > > > The sentence preceding Table 10.9 and the table tell you > what conversions are allowed and how the conversion is > done via a built-in intrinsic subprogram. > > It does tell you anything about an out-of-range value. > In fact, an INTEGER(KIND=1) entity has a range of > [-128,127], so the value of 256 is still out-of-range. > > As you have found, gfortran offers a programmer a bullet > to shoot their foot (i.e, the -fno-range-check option). > On most (all?) targets supported by gfortran, you'll get > two's complement wrap-around semantics. You do not get > truncation, where I assume you mean that an out-of-range > value is truncated to -128 or 127 as the situation would > merit (e.g., var8 = 257_2 <-- huge(var8) = 127). > > As to the "no warning problem", you did not ask gfortran > to generate warnings. You can use either the -Wall option > or the -Wconversion option to get a warning when using > the -fno-range-check option. > > %gfcx -o z -fno-range-check -Wall a.f90 > a.f90:2:33: > > 2 | integer(1), parameter :: var8 = 257_2 > | 1 > Warning: Conversion from 'INTEGER(2)' to 'INTEGER(1)' at (1) [-Wconversion] I should probably not continue with this issue, but I found the other text in the Standard. The intrinsic assignment of var8 = 257_2 with regards to Table 10.9 is then var8 = int(257_2, kind=1) But, the Fortran standard contains (18-007r1, p.339) A program shall not invoke an intrinsic procedure under circumstances where a value to be assigned to a subroutine argument or returned as a function result is not representable by objects of the specified type and type parameters. So, int(257_2, 1) is technically not permitted by the Fortran standard, and gfortran dutifully issues an error if you write such a conversion.
