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From: wyatt@cfa.UUCP (Bill Wyatt)
Newsgroups: net.math,net.lang.c,net.arch
Subject: Re: Re: Integer division
Message-ID: <177@cfa.UUCP>
Date: Fri, 31-Jan-86 10:20:06 EST
Article-I.D.: cfa.177
Posted: Fri Jan 31 10:20:06 1986
Date-Received: Sat, 1-Feb-86 20:33:35 EST
References: <332@ism780c.UUCP> <11603@ucbvax.BERKELEY.EDU>
Distribution: net
Organization: Harvard-Smithsonian Center for Astrophysics
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Xref: watmath net.math:2769 net.lang.c:7720 net.arch:2449


>  [ .... ]             In C on UNIX, for example, one has
> log(-x) == log(x), a rather dangerous identity, not based on anything
> comprehensible.  Thus, the implementation of general exponentiation,
> a**b = pow(a,b) = exp( b*log(a) ) will silently return the wrong value
> if a is negative.  (Try taking cube roots this way!)]
> 
> ucbvax!brahms!weemba	Matthew P Wiener/UCB Math Dept/Berkeley CA 94720

I did the above example (uVax II, Ultrix 1.1) and got a `floating exception'.
AHA, I thought , DEC cleaned up this bogosityr! Then I decided to simply
print log(-4.0), and it happily printed a garbage number!

It would seem that the exception was only because the exp function was 
delivered a large number.
-- 

Bill    UUCP:  {seismo|ihnp4|cmcl2}!harvard!talcott!cfa!wyatt
Wyatt   ARPA:  wyatt%cfa.UUCP@harvard.HARVARD.EDU