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Newsgroups: comp.lang.ada
Date: Mon, 21 May 2018 11:47:32 -0700 (PDT)
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Subject: Re: Should exceeding the range of Integer wrap around a la C?
From: Anh Vo <anhvofrcaus@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:52551
Date: 2018-05-21T11:47:32-07:00
List-Id: <comp.lang.ada>

On Monday, May 21, 2018 at 9:46:30 AM UTC-7, Simon Wright wrote:
> Anh Vo <anhvofrcaus@gmail.com> writes:
> 
> > On Monday, May 21, 2018 at 8:23:21 AM UTC-7, nrs...@gmail.com wrote:
> 
> >> I expect this program to print powers of 2 until `X` exceeds the
> >> range of Integer. Instead, it seems to "wrap around" with the
> >> following (abbreviated) output:
> >>           1
> >>           2
> >>           4
> >>       [...]          
> >>   268435456
> >>   536870912
> >>  1073741824
> >> -2147483648
> >>           0
> >>           0
> >>       [...]
> >>           0
> >> 
> >> I am compiling with GNAT 4.9.2 on a Debian Linux system using `gnat
> >> make compute` with no further compiler flags. Are my expectations
> >> wrong, or is this incorrect behavior?
> >
> > A Constraint_Error must be raised. If not, it is a compiler bug.
> 
> This isn't a bug, it's a feature of older GNATs; AdaCore thought that
> checking for overflow of machine integers would be too inefficient. The
> fact that (a) everyone puts -gnato in their options and (b) -gnato is
> now the default indicate that that thought was wrong (or, at any rate,
> became wrong a good while ago).

I rechecked the ARM 11.5 (16 and 27/2) again. You are correct. The implementer is allowed to suppress Overflow_Check instead of language required overflow check.