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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Should exceeding the range of Integer wrap around a la C?
Date: Mon, 21 May 2018 17:46:45 +0100
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Date: 2018-05-21T17:46:45+01:00
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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).