peculiar behavior: 64 byte integer in g77 and gfortran

[Tobias Burnus]

Dear Wang-Bin,

wangbin@shgentai.com wrote:
>                   integer *8 a,b
>                   a=2**60
> a. When I compile it with gfortran, the complier gfortran tell me
> 2**60    is    oarithhematic overrflow.
>   
There is indeed a arithmetic overflow, though it is a bit hidden:

1152921504606846976 = 2**60 is too big for a default-kind integer:
2147483647 = huge(1_4) although it fits into a 8-byte integer:
9223372036854775807 = huge(1_8)

You need to use 2_8**60 or int(2,kind=8)**60 or ... otherwise
you have a problem.

I tried the Intel Compiler with a similar program and it prints for
integer(8) :: a = 2**60
print '(i0)', a
end

fortcom: Warning: aa.f90, line 1: Overflow occurred while evaluating
constant expression.
integer(8) :: a = 2**60

If you indeed want the variable to overflow, you can use the option
-fno-range-check, but you likely get an undesired result. In your
specific case, 2_8**60 matches the result of a = 2**60 (without range
checking) by chance.

* * *

Regarding %loc(): gfortran currently only supports %loc() for actual
arguments. Thus

i = %loc(a) ! Not supported

does not work -- whereas the following works:

call sub(%loc(a)) ! Works

Tobias