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From: firth@sei.cmu.edu.UUCP
Newsgroups: comp.lang.c
Subject: Re: floating point ==
Message-ID: <907@aw.sei.cmu.edu.sei.cmu.edu>
Date: Thu, 9-Apr-87 09:09:44 EST
Article-I.D.: aw.907
Posted: Thu Apr  9 09:09:44 1987
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In article <429@euclid.warwick.UUCP> steve@warwick.UUCP (Steve Rumsby) writes:
>OK, now that we have decided that floating point == doesn't make a lot of sense
>and that feq(x, y, fuzz) is the way to go, does anybody have an *efficient*
>implementation of feq. I have an application spending between 10% and 15% of
>its time doing feq, and I would really like to speed up this routine. Any
>volunteers?

Allow me to pass on this disgusting hack with no recommendation
except that, when one of my students found it, it spread like wildfire:

. floating subtract y from x
. extract the exponent field of the result
. integer compare it to "small", where small = log2(eps)
  (don't forget the bias in the representation)

And you don't even have to worry about the sign of (x-y).  To make this
a closed subroutine, replace that last compare by a subtract.  The sign
of the result tells all.  Four instructions on a Vax.