[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <1367482359.28119.118.camel@eris.loria.fr>
Date: Thu, 02 May 2013 10:12:39 +0200
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: Re: sign (in)consistency between architectures
Am Mittwoch, den 01.05.2013, 22:47 -0400 schrieb Rich Felker:
> In any case, I think all of these issues are good arguments that
> nobodu should ever use clock_t or the clock() function...
Hm, AFAIR clock() is the only available function in C alone (including
C11) that gives access to something like the "processor time". C11 a
bit more of time handling to have access to something like a real time
clock, but for processor time clock() is the only one. (MS got that
wrong, but this is their problem.)
So I think it still makes sense to use it for "short" measures, not
for the whole run of a program. The standard suggests, I think, that
you'd take a point of measure before and after the interval that
interests you. For such a strategy to work you'd either have to know
that no overflow can reasonably occur (by having a wide type) or that
it may do no harm (by using an unsigned type).
I would prefer to have both worlds by using uint64_t (or directly the
underlying base type) uniformly. There is no reason to have it signed:
- this is "processor time" and not wallclock time, so it should be
monotonic, and not be affected by setting the system time
- an application should always subtract the first value of a measure
from the second
- an application should never expect to be able to measure intervals
that are longer than a few hours, and it can deduce the maximum
time it has for a measure with CLOCKS_PER_SEC
Jens
--
:: INRIA Nancy Grand Est :: http://www.loria.fr/~gustedt/ ::
:: AlGorille ::::::::::::::: office Nancy : +33 383593090 ::
:: ICube :::::::::::::: office Strasbourg : +33 368854536 ::
:: ::::::::::::::::::::::::::: gsm France : +33 651400183 ::
:: :::::::::::::::::::: gsm international : +49 15737185122 ::
Download attachment "signature.asc" of type "application/pgp-signature" (199 bytes)
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
