On Sat, 28 May 2011 23:12:54 -0700, John Nagle wrote:
> The correct answer to "nan == nan" is to raise an exception, because
> you have asked a question for which the answer is nether True nor False.
Wrong.
The correct answer to "nan == nan" is False, they are not equal. Just as
None != "none", and 42 != [42], or a teacup is not equal to a box of
hammers.
Asking whether NAN < 0 could arguably either return "unordered" (raise an
exception) or return False ("no, NAN is not less than zero; neither is it
greater than zero"). The PowerPC Macintishes back in the 1990s supported
both behaviours. But that's different to equality tests.
> The correct semantics for IEEE floating point look something like
> this:
>
> 1/0 INF
> INF + 1 INF
> INF - INF NaN
> INF == INF unordered
Wrong. Equality is not an order comparison.
--
Steven
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