Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!pyramid!mikel
From: mikel@pyramid.pyramid.com (Mike Lipsie)
Newsgroups: comp.lang.fortran
Subject: Re: extensions to logical variables
Keywords: vax,logicals
Message-ID: <67924@pyramid.pyramid.com>
Date: 27 Apr 89 16:13:20 GMT
References: <31660@stellar.UUCP>
Reply-To: mikel@pyramid.pyramid.com (Mike Lipsie)
Organization: Pyramid Technology Corp., Mountain View, CA
Lines: 20

In article <31660@stellar.UUCP> keith@stellar.UUCP (Keith Crews @stellar) writes:
>I have some questions about common fortran extensions to logical variables.
>
>The basic problem I have with the vax implementation is that I think that 
>a logical variable should always be true or false.  You can do this by 
>forcing a conversion to 0 or -1 when assigning to them (although this can 
>be defeated by using equivalences) or you can treat all non-zero logicals 
>as being true and only 0 as being false.  

Not answering Keith's question but rather pointing out an erroneous
assumption.  People who come from the C world seem to have internalized
false-true as zero-nonzero; those from Pascal as zero-one.  Other
implementations are possible.  A relatively common method is even-odd
because some machines had a fast low-order bit test; likewise, there
is positive-negative because of a fast sign bit test.

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Mike Lipsie                                         mikel@pyramid.com
Pyramid Technology Corp, Mountain View, CA  +1 415 965 7200 ext. 4980