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  Java & integer Overflow  (Read 1049 times)
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Offline Abuse

JGO Knight


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falling into the abyss of reality


« Posted 2007-03-26 18:29:05 »

Does anybody ever wish Java detected & reported integer overflow (via some kind of ArithmeticException) ?

For there to be no compile time, or runtime checking for this fail-slow error seems to me to be a serious limitation in the construction of complex systems.
The simplest assumption that many people fall foul of :-
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assert Math.abs(val)>=0;

The above assertion will fail when val = Integer.MIN_VALUE (as it will overflow round to itself)

A very common application of this flawed assertion would be :-

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Math.abs(random.nextInt())%range

Which will lead to an erroneous value being generated every 1 in ~4294967296 executions.
While the above is poor code (in both J2ME & J2SE), I have seen many examples of its usage.

Another common situation where overflow becomes a brain melter is when using FixedPoint libraries  Embarrassed

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Offline t_larkworthy

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« Reply #1 - Posted 2007-03-26 19:04:18 »

If all my code failed one in 4294967296 times, I would be a happy and probably rich man.

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Offline Riven
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« Reply #2 - Posted 2007-03-26 19:15:47 »

PITA, but if you want to be sure....

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         int a = ...;
         int b = ...;
         int c = a * b;

         assert ( ((a >>> 31) ^ (b >>> 31)) == (c >>> 31) );



Eh... which works... for 'quite a few' cases Smiley (damn double int overflow)

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