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From: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Newsgroups: comp.lang.c++
Subject: Re: bug in GNU C++ on sun386i
Message-ID: <PCG.90Aug17185750@athene.cs.aber.ac.uk>
Date: 17 Aug 90 17:57:50 GMT
References: <27519@nigel.ee.udel.edu>
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In-reply-to: willey@udel.edu's message of 15 Aug 90 13:19:49 GMT

On 15 Aug 90 13:19:49 GMT, willey@udel.edu (Edward V Willey) said:

willey> Help!  I am having *serious* problems with my C++ compiler and
willey> was wondering if anyone out there could help me?...

I very much doubt the problem is serious; and most probably it is not
with the compiler, or C++.

willey> [ ... the description of some problem with his machine or
willey> program ...  ]

From your report you allege that the same identical program compiled
twice gives different results. You allege that this must be a fault of
the compiler. This is *impossible*, because the possible causes of non
deterministic behaviour by a program are;

1)	The hardware is non deterministic
2)	The compiler is time dependent
3)	The program is time dependent

I am willing to bet that 2) is not true (note that an erroneus compiler
will still be deterministic, if it is not time dependent internally). If
1) is true, and you are working on stock hardware, this means that it is
faulty, because stock hardware is supposed to be deterministic (or at
worst slightly time dependent).

willey> PS.  Some friends and I came up with a possible reason.  We
willey> believe that there is a major undocumented feature of GNU.  We
willey> call it RDCI: Random Dynamic Code Interpretation.  Who knows
willey> what the seed is? (it's probably random itself!)

So either your machine is broken, or your program is broken, or your
analysis is broken (i.e. you did not compile exactly the same program).
Note that the compiler is known to have bugs, but they are deterministic
ones (unless Tiemann changed the implementation radically and made it
time dependent).

My hunch is that your analysis is broken (because you seem to ignore
that most compilers, and certainly GNU C++, are deterministic in their
erroneous behaviour), or failing that the machine is broken (major
source of indeterminate behaviour).

	note: I know that non deterministic and time dependent are not
	the same thing, but please pass over it now; substitute 'seemingly
	non determinstic' above where appropriate.
	
--
Piercarlo "Peter" Grandi           | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcsun!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk