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From: Dr J R Stockton on 4 Jun 2010 13:03


A variable of type Number always has a detectable sign, except when
its value is NaN. Some experienced programmers, and many others, do not
know how to determine this sign in all cases. Therefore I suggest a new
ECMA Global Function, returning a zero value for NaN, +1 for anything
else with the sign bit clear, and -1 for anything else with the sign bit
set.

To determine the sign of any non-NaN Number X, it seems to me that
one can form X+1/X and compare with zero. The following Sign function
also handles NaN. Test :

Arr =
[-Infinity, -1.0, 1/-Infinity, -0, NaN, +0, 1/+Infinity, +1.0, +Infinity]

function Sign(X) { X += 1/X ; return (X > 0) - (X < 0) }

function FF(A) { for (var J = 0 ; J < A.length ; J++) A[J] = Sign(A[J]) }

FF(Arr) // NOW, Arr = [-1, -1, -1, -1, 0, +1, +1, +1, +1]


--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
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