`Kai, hello.`
`On 25 Jul 2007, at 10:57, Kai Hackemesser wrote:`
` a number is true if and only if it is neither positive or
negative`

zero nor NaN<<

`My problem may be just lack of english language, but I need some
explanation here. What is meant by positive or negative zero? From
my math understandings zero is neither positive nor negative. If I
drop that and say, a number is true when the value is neither zero
nor NaN, would this be correct?
`

On essentially all significant hardware these days, floating point
numbers are represented according to the IEEE 754 standard[1].
Amongst other things, that includes special bit patterns for positive
and negative infinity, a large set of bit patterns for NaN (not-a-
number), and the property that zero can be signed, so that 1.0*0.0=
+0.0 and -1.0*0.0 = -0.0. The distinction matters in certain
numerical contexts, but is ignorable for everyone else.
`All the best,`
`Norman`
`[1] http://en.wikipedia.org/wiki/IEEE_754`

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Norman Gray : http://nxg.me.uk
eurovotech.org : University of Leicester, UK