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From: ags@s.cc.purdue.edu (Dave Seaman)
Newsgroups: comp.lang.fortran
Subject: Re: CDC FORTRAN trivia questions
Keywords: arithmetic if logical
Message-ID: <3616@s.cc.purdue.edu>
Date: 31 Oct 88 15:33:27 GMT
References: <1196@helios.ee.lbl.gov>
Reply-To: ags@s.cc.purdue.edu.UUCP (Dave Seaman)
Organization: Purdue University
Lines: 47

In article <1196@helios.ee.lbl.gov> mike@quench.lbl.gov (Michael Helm) writes:
	[Re:  Ancient CDC Fortran and the two-branch logical IF]

	[This is my corrected posting.  I have cancelled an incorrect
	earlier posting.  If you see another posting from me on this
	subject, ignore it.]

>        LOGICAL IRON
>   .
>   .
>   .
>        IF(IRON)4,9
>
>What logical state will IRON be in for #4 to be executed, & for #9
>to be executed?  

The Fortran 77 equivalent of this CDC-ism is:

	 IF (IRON) THEN
	   GO TO 4
	 ELSE
	   GO TO 9
	 ENDIF

CDC compilers also recognized a two-branch arithmetic IF of the form,

	IF (aexp) 10,20

where "aexp" is an arithmetic expression.  The Fortran 77 equivalent is:

	IF (aexp .NE. 0) THEN
	  GO TO 10
	ELSE
	  GO TO 20
	ENDIF

>How were(are) logical values represented on old(current)
>CDC hardware or in CDC FORTRAN programs?

The representation of logical values is a software concept, not a hardware
concept.  I can't imagine why you would need to know the representation
chosen by a particular Fortran compiler, but if I remember correctly, the
usual convention was to represent .TRUE. as -1 and .FALSE. as zero.  Some
of the very old CDC compilers used a different convention.
-- 
Dave Seaman	  					
ags@j.cc.purdue.edu