Re: Constraint_Error in arithmetic expressions

[Michal Nowak <vinnie@inetia.pl>]

On 2003-01-12 at 23:37 Robert A Duff wrote:

>> Suppose that if I declare:
>>    type T is range 1 .. 200;
>>    A : T := 150;
>>    B : T := 150;
>> the compiler may choose 1 byte (0 .. 255) or 2 bytes (0 .. 65535) for
>> example, for the base subtype.
>
>No.  "is range" declares a signed integer type, and for signed integers,
>the base range is always symmetric about zero (or has an extra negative
>value).  So the minimal base range the compiler can choose in this case
>is -200..200.  It can choose a wider range.  Compilers usually choose a
>range that is supported by the hardware.

Oh, in fact, I found appropriate RM section.

Now comes another curious question -
Why the base range is symmetric about zero?
Is it because that it is for signed integer? Are there any reasons 
for it?
I'm asking, because suppose I have a 16 bit machine. 
Now I want to declare:
   type T is range 2**16 - 10 .. 2**16 - 1;

but it is not possible. However, if the base type could be in range
0 .. 2**16 - 1 it could be possible.

Thank you for your previous answer,
  - Michal


"Beyond 100,000 lines of code you
should probably be coding in Ada"
   - P. J. Plauger