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From: lippin@wheatena.berkeley.edu (The Apathist)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Severe Bug in SANE Package ?
Message-ID: <21046@agate.BERKELEY.EDU>
Date: 1 Mar 89 23:09:41 GMT
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Recently roh@gmdzi.UUCP (Peter Rohleder ) wrote:
>
>It seems that we have found a severe bug in the Apples SANE-Package.
>
>We found it when we tried to figure out whether an EXTENDED has
>digits unequal zero behind a predefined position after the decimalpoint.
[...]
>Is this really a severe bug in the SANE-Package or is there anything wrong
>in our understanding of the precision of the different operations in SANE.

I don't think this is really a bug; the problem lies in the necessary
inaccuracy of applying the decimal concept of digits to the binary
representations of SANE.

In your relation test, you are (correctly) using a fudge factor in the
check for equality, to avoid errors in the last few bits.  However,
you neglect to scale the fudge factor along with the numbers you are
comparing, and so when you multiply by 10000, the errors in
representation become greater than your saftey margin.  I suspect,
though I haven't tried it, that if you raise kDelta to 1E-14 your
example program will work.

					--Tom Lippincott
					  lippin@math.berkeley.edu

	"Thank you for observing all saftey precautions."
					--Dark Star