Path: csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!news.linkpendium.com!news.linkpendium.com!teleglobe.net!newsgate.cuhk.edu.hk!news.netfront.net!not-for-mail
From: Wanja Gayk <brixomatic@yahoo.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Arithmetic overflow checking
Date: Wed, 6 Jul 2011 22:28:50 +0200
Organization: Netfront http://www.netfront.net/
Lines: 80
Message-ID: <MPG.287ee3d2698d83599896a9@202.177.16.121>
References: <015aeb15-57db-48ab-9cd4-77f8448b632f@w24g2000yqw.googlegroups.com>
NNTP-Posting-Host: 217.191.7.71
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Trace: adenine.netfront.net 1309984128 64283 217.191.7.71 (6 Jul 2011 20:28:48 GMT)
X-Complaints-To: news@netfront.net
NNTP-Posting-Date: Wed, 6 Jul 2011 20:28:48 +0000 (UTC)
User-Agent: MicroPlanet-Gravity/3.0.4
Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:5921

In article <015aeb15-57db-48ab-9cd4-
77f8448b632f@w24g2000yqw.googlegroups.com>, rop049@gmail.com says...
> 
> Hi,
> 
> If I want to have arithmetic-overflow checking in all parts of an
> application,
> what is the most practical, simple, efficient way to achieve this?
> Id like to clutter the code as little a possible...
> Is there any way to instruct the JVM to include it?

Not automagically, at least if you want to avoid building a sourcecode-
preprocessor or tool that instruments your bytecode at class loading 
time.

You could use your very own math-methods and discourage the use of the 
operators "+","-" throughout your code by convention.

public final class OverflowUtil{

 public static void passIntRangeCheck(final long x){
  if( x > Integer.MAX_VALUE)
   throw new ArithemticException("int overflow");
  if if( x < Integer.MIN_VALUE)
   throw new ArithemticException("int underflow");
 }

 public static void passLongRangeCheck(final BigInteger x){
  if( x.compareTo(BigInteger.valueOf(Long.MAX_VALUE)) > 0)
   throw new ArithemticException("long overflow");
  if( x.compareTo(BigInteger.valueOf(Long.MIN_VALUE)) < 0)
   throw new ArithemticException("long underflow");
 }

 //... same for byte and short
}


import static OverflowUtil.*;
public class OverFlowSafe{

 static int add(final int a, final int b){
  final long x = a+b;
  passIntRangeCheck(x);
  return (int)x;
 }

 static long add(final long a, final long b){
   final long x = BigInteger.valueOf(a).add(BigInteger.valueOf(b);
   passLongRangeCheck(x);
   return x.longValue();
 }

 //.... other operations..
}

To be used like:

void foo(){
  final int x = Integer.MAX_VALUE;
  final int y = 1L;
  final int sum = OverflowSafe.add(x,y);

  System.out.println(sum);
}

The code not tested and hacked in a hurry, varargs would probably be 
nicer. The upside to any instrumentation or preprocessing tool is that 
you can distinguish safe from unsafe code with a blink of an eye.

Kind regards,
Wanja

-- 
..Alesi's problem was that the back of the car was jumping up and down 
dangerously - and I can assure you from having been teammate to 
Jean Alesi and knowing what kind of cars that he can pull up with, 
when Jean Alesi says that a car is dangerous - it is. [Jonathan Palmer]

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---