Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!necntc!ima!johnl
From: johnl@ima.ISC.COM (John R. Levine)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran follies
Message-ID: <1028@ima.ISC.COM>
Date: 19 May 88 02:00:17 GMT
References: <5377@cup.portal.com> <50500052@uxe.cso.uiuc.edu> <705@thalia.rice.edu>
Reply-To: johnl@ima.UUCP (John R. Levine)
Organization: Not much
Lines: 33

In article <705@thalia.rice.edu> david@titan.UUCP (David Callahan) writes:
>In article <50500052@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes:
>>
>>        real x(100000)
>>        call sub(1000, x(1),x(10000),x(20000))
>>        ...
>>        subroutine sub(n,x,y,z)
>>        dimension x(n), y(n), z(n)
>>	  ...
>Very common (probably essential to making libraries) but not legal;
>
>"15.9.3.6 Restrictions on Association of Entities. If a subprogram reference
>causes a dummy argument in the referenced subprogram to become associated with
>another dummy argument in the referenced subprogram, neither dummy argument
>may become defined during execution of that subprogram. ...

By my reading of the F77 standard, it's perfectly legal to pass disjoint
chunks of an array to a subprogram as separate arguments. 2.14 says that
association means that the same datum may be identified by different symbolic
names. The discussion of association of storage sequences and entities in
17.1.2 and 17.1.3 makes it pretty clear that two arrays are associated iff
their storage overlaps; in this case they don't so 15.9.3.6 doesn't apply.

Intuitively, the restriction in 15.9.3.6 is intended to prohibit argument
aliasing that would break calling sequences that copy in argument values at
call time and copy changed results back before the return. In this case, even
if the arrays were passed by copy/return (pretty unlikely for an array, but
still legal) the code would still work.

Scripturally yours,
-- 
John R. Levine, IECC, PO Box 349, Cambridge MA 02238-0349, +1 617 492 3869
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