Re: Arithmetic overflow checking

In article <015aeb15-57db-48ab-9cd4-
77f8448b632f@w24g2000yqw.googlegroups.com>, rop049@gmail.com says...


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

--
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