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From: riley@theory.TC.Cornell.EDU (Daniel S. Riley)
Newsgroups: comp.sys.mips
Subject: Re: f77 compiler bug (both MIPS and SGI)
Message-ID: <1991Jun19.162129.2870@batcomputer.tn.cornell.edu>
Date: 19 Jun 91 16:21:29 GMT
References: <1991Jun17.224729.15190@rice.edu> <1991Jun18.191622.4008@odin.corp.sgi.com> <1991Jun19.133207.24629@cpsc.ucalgary.ca>
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In article <1991Jun19.133207.24629@cpsc.ucalgary.ca>,
cliff@phys.ucalgary.ca writes:
>>>I've discovered an interesting 'glitch' in the f77 compiler for
>>>MIPS (and consequently, for SGI, also). given a code skeleton of :
>>>
>>>   if (...) goto 10
>>>      .
>>>   do 10 ....
>>>      .
>>>10 continue

>  Many thanks to all that pointed out that jumping into a loop is illegal.  
>  But strictly speaking, the above is not illegal.  Older f77 compilers 
>  understood that this meant to skip over the code from the 'if' to the 
>  '10 continue'.  (example: the 4.3BSD (circa '87) compiler handles this 
>  code just fine and produces the *correct* results.  Anyway, it really 
>  just a look into the past (f66) since it is bad coding style! {-8

Just because some compiler accepts it and does what you want does
not mean that it is legal code.  To quote chapter and verse, from
ANSI X3.9-1978 (FORTRAN 77),

page 11-6,

	11.10.1 Range of a DO-Loop.  The range of a DO-Loop consists of
	all of the executable statements that appear following the DO
	statement that specifies the DO-Loop, up to and including the
	terminal statment of the DO-Loop.

and page 11-9,

	11.10.8 Transfer into the range of a DO-Loop.  Transfer into the
	range of a DO-Loop from outside of the loop is not permitted.

Since the terminal statement is part of the range of the DO-Loop, the code
above is unambiguously illegal, strictly speaking, according to the ANSI
FORTRAN 77 standard.
-- 

-Dan Riley (riley@theory.tc.cornell.edu, cornell!batcomputer!riley)
-Wilson Lab, Cornell University