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Re: RFA/PATCH gtest - NSNumber float != double

From: David Ayers
Subject: Re: RFA/PATCH gtest - NSNumber float != double
Date: Tue, 21 Jan 2003 23:04:33 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3a) Gecko/20021212

Alexander Malmberg wrote:

David Ayers wrote:
Hello everyone,

I'm working on a set of GDL2 guile tests and ran into a base issue.
+numberWithFloat: 25.1 and +numberWithDouble: 25.1 are not equal.  I've
attached an patch for gtest on this issue which also updates some other
changes in the general configuration.

This is expected. 25.1 can not be represented exactly as a floating
point number. When you create a float 25.1, you get the float-number
closest to 25.1, and when you create a double 25.1, you get the
double-number closest to 25.1. These usually aren't the same, so the
comparison is correct.

Hmm, I'll take your word for it. I just recalled back in the dark ages someone told me (or I read it somewhere) that 25.1 would somehow be represented as 2.51 * 10^1 and that a float or double only stored the mantissa and exponent which shouldn't result in any discrepancies here. But maybe that was just some illustration of principle. (I wonder how Apple deals with this... I'll check tomorrow.)


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