Path: utzoo!utgpu!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: <7706@boring.cwi.nl>
Date: 5 Nov 88 22:53:53 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> <16427@agate.BERKELEY.EDU>
Organization: CWI, Amsterdam
Lines: 14

In article <16427@agate.BERKELEY.EDU> forags@violet.berkeley.edu writes:
 > 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...)
 > 
This explains it.  I would never have thought that a compiler writer would use
that instruction for logicals.  Interestingly, on many Cybers the sequence I
gave (OR(NOT(L)+0,L).GE.0) is faster than CXi Xk followed by a PL, and does
the same!  And if you follow comp.arch you know why this instruction was there.
-- 
dik t. winter, cwi, amsterdam, nederland
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