From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 15227 invoked by alias); 29 Dec 2014 15:04:08 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 15187 invoked by uid 48); 29 Dec 2014 15:04:03 -0000 From: "anlauf at gmx dot de" To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/64432] [5 Regression] SYSTEM_CLOCK(COUNT_RATE=rate) wrong result for integer(4)::rate Date: Mon, 29 Dec 2014 15:04:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: fortran X-Bugzilla-Version: 5.0 X-Bugzilla-Keywords: wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: anlauf at gmx dot de X-Bugzilla-Status: NEW X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: fxcoudert at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2014-12/txt/msg02862.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64432 --- Comment #5 from Harald Anlauf --- (In reply to Francois-Xavier Coudert from comment #4) > I'm not sure this is a bug, but this was definitely by design (as the > comment indicates). I think this is allowed by the successive standards > (which are, in any case, very weakly worded). Well, let's see: the standard says: COUNT RATE (optional) shall be an integer or real scalar. It is an INTENT (OUT) argument. It is assigned a processor-dependent approximation to the number of processor clock counts per second, or zero if there is no clock. You're right, it does not say anything about consistency. Nevertheless, I would prefer if a program that always uses e.g. default integer == integer(4), the low-resolution (msec) version continues to be used consistently. That's what other compilers do and what gfortran <= 4.9 did. Also, the presence of a second argument (see comment #1) should not change the behavior. OTOH, it is the responsibility of a user to consistently use arguments of the same type and kind to get consistent behavior. (I.e. not mixing integer and real or integer(4) and integer(8)). I do take care of that. > The root of the problem is that we want to allow for SYSTEM_CLOCK to return > high-precision values for large integer kinds, and fall back to > lower-precision results that fit in fewer bytes for smaller integer kinds. How is this fallback done? Do you truncate the resolution? E.g. high res. -> low res.: divide count_rate and count by 1000? > Thus, one should call SYSTEM_CLOCK once with all the necessary arguments, > and not multiple times with varying argument types. Note that I did *not* call SYSTEM_CLOCK with varying argument types. You're probably not aware of existing (f95) code that deals with the problem of wrapping, which is always present (count does not necessarily start with 0 at start of the program), although not very likely with integer(8)... ;-) > The only other consistent option I can see would be to simply go for > high-resolution results in all cases, but that would mean that SYSTEM_CLOCK > with 32-bit integers would wrap around in less than an hour. No, that doesn't make sense. > If you have another idea, please post a list of what you think should happen > in all various cases (all possible combinations of arguments have to be > allowed). Let's see: - For any number of arguments present (1, 2 or 3) - always integer(4): msec resolution (as before) - always integer(>=8): usec resolution (or whatever is possible) - always real: I don't care, but I think it might be a good idea to use the same as for integer of a compatible kind. - different types and/or kinds: I don't care, since one should expect problems (wrapping or truncation) anyway. But presence of non-presence should never make a difference if consistent types and kinds are used.