Result of ``a is b''

[Erik Max Francis]

Andrew Koenig wrote:

> I'm pretty sure that IEEE floating point requires NaN to be defined in
> such
> a way that if x is NaN, then x == x must yield False.

That's correct.  Python itself doesn't do this, though:

Python 2.3.3 (#1, Dec 22 2003, 23:44:26) 
[GCC 3.2.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 1e3000
>>> a
inf
>>> a/a
nan
>>> n = a/a
>>> n == n
True
>>> 

[Similar things are shown for Python on Solaris 8.]

But the following C program:

#include <stdio.h>

int main(void)
{
    double a = 1e3000;

    double n = a/a;

    printf("%f, %f, %d\n", a, n, a == n);

    return 0;
}

prints

inf, nan, 0

on Intel Linux.

-- 
 __ Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/
/  \ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
\__/ Chance favors the trained mind.
    -- Louis Pasteur