Date: Thu, 28 Feb 2013 11:46:14 -0500 From: Ryan Stone <rysto32@gmail.com> To: Alexey Dokuchaev <danfe@freebsd.org> Cc: Davide Italiano <davide@freebsd.org>, svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r247460 - head/sys/dev/acpica Message-ID: <CAFMmRNyCB1PC5zQ1448PyxcoXRUwqLKfooOoQ9dKJ4RDFgJ6sQ@mail.gmail.com> In-Reply-To: <20130228162522.GA41693@FreeBSD.org> References: <201302281127.r1SBR2VE068276@svn.freebsd.org> <20130228162522.GA41693@FreeBSD.org>
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On Thu, Feb 28, 2013 at 11:25 AM, Alexey Dokuchaev <danfe@freebsd.org>wrote: > On Thu, Feb 28, 2013 at 11:27:02AM +0000, Davide Italiano wrote: > > New Revision: 247460 > > URL: http://svnweb.freebsd.org/changeset/base/247460 > > > > Log: > > MFcalloutng (r247427 by mav): > > We don't need any precision here. Let it be fast and dirty shift then > > slow and excessively precise 64-bit division. > > > > - if (sbt >= 0 && us > sbt / SBT_1US) > > - us = sbt / SBT_1US; > > + if (sbt >= 0 && us > (sbt >> 12)) > > + us = (sbt >> 12); > > Does this really buy us anything? Modern compilers should be smart enough > to > generate correct code. Do you have evidence that this is not the case > here? > Not to mention that it obfuscates the code by using some magic constant. > > ./danfe > SBT_1US is 4294, not 4096 (1 << 12). This is an approximation, which the compiler obviously can't automatically apply.
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