Path: utzoo!attcan!uunet!mcvax!dik
From: dik@cwi.nl (Dik T. Winter)
Newsgroups: comp.lang.fortran
Subject: Re: CDC FORTRAN trivia questions
Keywords: arithmetic if logical
Message-ID: <7709@boring.cwi.nl>
Date: 8 Nov 88 16:34:34 GMT
References: <1196@helios.ee.lbl.gov> <3616@s.cc.purdue.edu> <7523@ut-emx.UUCP> <3622@s.cc.purdue.edu> <7693@boring.cwi.nl> <3627@s.cc.purdue.edu> <2183@tekcae.CAX.TEK.COM> <7588@well.UUCP>
Organization: CWI, Amsterdam
Lines: 16

In article <7588@well.UUCP> rchrd@well.UUCP (Richard Friedman) writes:
 > The comment was made that CDC hardware prevented -0 from being
 > generated.  This was/is true, but there were times the FTN4 and
 > FTN5 math library routines would (for specific arguments) return -0.
 > This was a hard error to find, but eventually it got corrected.
 > 
Not exactly true; floating-point and integer arithmetic do not generate -0,
if the input operands do not contain -0.  But otherwise they can be generated.
E.g. truncating a negative floating point value to integer (if between -1.0
and 0.0).  Also overflowing integer multiply (which is really a special case
of floating-point multiply) can return -0.  Most compilers compensate
for this by adding +0 to the result, which turns -0 to +0.
-- 
dik t. winter, cwi, amsterdam, nederland
INTERNET   : dik@cwi.nl
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