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From: forags@violet.berkeley.edu
Newsgroups: comp.lang.fortran
Subject: Re: CDC FORTRAN trivia questions
Keywords: arithmetic if logical
Message-ID: <16427@agate.BERKELEY.EDU>
Date: 3 Nov 88 02:48:41 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>
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In article <3627@s.cc.purdue.edu> ags@s.cc.purdue.edu.UUCP (Dave Seaman) writes:
>
>The RUN compiler did indeed use this scheme.  It is true that the hardware
>compare for zero gets both +0 and -0, but all this proves is that the RUN
>compiler did not use the hardware compare for zero when testing logicals.
>
Right!  The RUN compiler used a CXi Xk instruction (count all one-bits in Xi
and store the result in Xk, so anything but 60 zero bits was true). (On a 
6000-series machine this took an obscene number of minor cycles (68 on a
6400), which made logical variables rather slow to evaluate...)


Al Stangenberger                    Dept. of Forestry & Resource Mgt.
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