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Path: utzoo!linus!philabs!mcvax!guido
From: guido@mcvax.UUCP (Guido van Rossum)
Newsgroups: net.bugs
Subject: C log function inaccurate (with fix) (many UNIX versions)
Message-ID: <5582@mcvax.UUCP>
Date: Thu, 5-Jan-84 15:20:55 EST
Article-I.D.: mcvax.5582
Posted: Thu Jan  5 15:20:55 1984
Date-Received: Sat, 7-Jan-84 11:16:15 EST
Organization: Math.Centre, Amsterdam
Lines: 21

One of my colleagues discovered that the log function the the mathematical
C library is quite inaccurate.  What's more, he also provided a change
to one of the coefficients which much improved it.  Here they are:

BAD:  p2 = -.963769093368686593e1;
GOOD: p2 = -.963769093377840513e1;
                       ^^^^^^^^

So now you should all go and fix your C library.
I found the same coefficients in UNIX V7 as in 4.2 BSD, so I suspect
they are probably in almost all other UNIXes around the world.

Related question: the source states
	"The coefficients are #2705 from Hart & Cheney. (19.38D)".
We cannot locate this reference in our institute's library.
Does someone know what this references, and give us a more precise pointer?

Guido van Rossum, {philabs,decvax}!mcvax!guido
Centre for Mathematics and Computer Science, (CWI, formerly MC), Amsterdam

(with thanks to Lambert Meertens)