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Date: Mon, 25 Jul 2011 09:30:16 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: Arithmetic overflow checking
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On 7/25/2011 9:09 AM, Patricia Shanahan wrote:
...
> The key question is how "sensible" is the correspondence. We already
> have some awkwardness in making Double implement Comparable and extend
> Number, because Double can have Not-a-Number values. Double has to
> pretend NaNs are numbers in some Comparable and Number contexts, even
> though their whole point is to represent the lack of a numerical result.
...

Returning to the original topic of this thread, I think one of the worst
decisions in the early Java design was to treat NaN as zero on
conversion to an integer type.

Consider the following program:

public class DivisionExample {
   public static void main(String[] args) {
     System.out.println(0.0 / 0.0);
     System.out.println((long) (0.0 / 0.0));
     try {
       System.out.println(0 / 0);
     } catch (ArithmeticException e) {
       System.out.println("Integer division: " + e.getMessage());
     }
   }
}

It prints:

NaN
0
Integer division: / by zero

If the undefined 0/0 division is done in an integer type it throws an
exception. If it is done in double and the double is output as a double,
it is a NaN. If the double is converted to integer, the already detected
NaN condition is silently turned into a zero.

Patricia