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Comment by nemothekid | Hacker News Reader

The stupid thing about IEEE NaN is that it's not equal to itself!

Why would it be? The rationale makes perfect sense. It would be unexpected to believe that 17/0 == 0^0. Both are NaN, and equally nonsense, but 2 very different statements.

Secondly, IIRC, NaN is supposed to break assert(x==x), because if you use NaN in your program, then your program is undefined.

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Your == expression has distinct operands which are the results of different evaluations.

The problem is that a NaN is not equal to itself:

    double nan = /* NaN-producing expression */

    if (nan == nan) {
      /* dead code */
    }

While your overall point is correct, your example is wrong: 17/0 == Infinity, and 0^0 == 1. Neither is NaN :)

Infinity is Not a Number, so 17/0 is NaN.

IEEE floating point distinguishes infinities and NaNs.

D'oh. Missed that we were specifically talking about IEEE floating point. That was very stupid of me.

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