Re: Optimizing and Constraint Checks

[l107353@cliffy.lfwc.lockheed.com (Garlington KE)]

Ed Bruce (edward@igate1.hac.com) wrote:
: I am currently attempting to implement a safe, portable
: Unchecked_Conversion of an enumerated type to integer and from an integer
: type back to the enumeration. The following code shows the current
: solution, the question raised by one engineer is can we guarantee the the
: return statement in the To_Enum function is portable. That is may a
: compiler optimize away the ENUM'Pos and ENUM'Val and effectively eliminate
: the constraint check.

I think your first portability problem is whether the ENUM will fit into an
INTEGER. My compiler manual says: "Objects of enumeration types are allocated
one word when no representation specification is given. If a specification
is given that uses values in the range of LONG_INTEGER (but outside the
range of INTEGER), objects will be allocated in double words.

Second, I could definitely see a compiler optimizing away 'Val('Pos). 'Valid
would be a better attribute here.

Third, if an enum spec is used, I'm not sure what happens if there are holes
in the underlying number sequence. The LRM says that CONSTRANT_ERROR is
raised if X'Val is not in the _range_ T'POS(T'BASE'FIRST) ..
T'POS(T'BASE'LAST). If it's in range, but not a valid representation, I
suspect different compilers might behave differently.

--------------------------------------------------------------------
Ken Garlington                  GarlingtonKE@lfwc.lockheed.com
F-22 Computer Resources         Lockheed Fort Worth Co.

If LFWC or the F-22 program has any opinions, they aren't telling me.