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From: Martin Gregorie <martin@address-in-sig.invalid>
Newsgroups: comp.lang.java.programmer,comp.lang.c
Subject: Re: Arithmetic overflow checking
Date: Tue, 12 Jul 2011 16:54:36 +0000 (UTC)
Organization: UK Free Software Network
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On Tue, 12 Jul 2011 09:26:49 -0700, markspace wrote:

> On 7/12/2011 6:16 AM, Stefan Ram wrote:
>> "BartC"<bc@freeuk.com>  writes:
>>> a+b overflows, but then what?
>>
>>    This can only be answered given the requirements specification of a
>>    specific project.
> 
> 
> What I think he's saying is there's no way physically detect the
> overflow in a language like C which has no exceptions.  You'd have to at
> least introduce some sort of global flag.
> 
>    int c = a + b;
>    if( GLOBAL_OVERFLOW_FLAG ) {
>      printf( "bugger..." );
>    }

Interestingly, the much maligned COBOL has a built-in mitigation for 
overflow and a way of trapping it:

Mitigation: since you can specify the number of digits in a numeric data 
item (integer or fixed decimal), it follows that the programmer can 
control whether overflow can occur and, as the maximum size of a numeric 
field is 18 digits, the result field can almost alrays be made long 
enough.

Trapping: all computational verbs will accept the ON SIZE ERROR clause 
which, despite its name, traps almost all possible calculation errors 
including overflow, divide by zero, etc.:

ADD TRANSACTION-VALUE TO TOTAL-VALUE 
    ON SIZE ERROR PERFORM REPORT-CALCULATION-ERROR.

...and yeah, whoever it was who said Java was verbose has clearly never 
written COBOL!


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
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