Date: Tue, 22 Nov 2011 12:09:19 -0500 From: John Baldwin <jhb@freebsd.org> To: David Schultz <das@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Eitan Adler <eadler@freebsd.org> Subject: Re: svn commit: r227812 - head/lib/libc/string Message-ID: <201111221209.19728.jhb@freebsd.org> In-Reply-To: <20111122153332.GA20145@zim.MIT.EDU> References: <201111220250.pAM2oPWC070856@svn.freebsd.org> <20111122153332.GA20145@zim.MIT.EDU>
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On Tuesday, November 22, 2011 10:33:32 am David Schultz wrote: > On Tue, Nov 22, 2011, Eitan Adler wrote: > > + /* use a bitwise or to avoid an additional branch instruction */ > > + if ((s1 == s2) | (n == 0)) > > + return (0); > > I think there are three issues with this. > > First, the comment suggesting that using '|' instead of '||' isn't > correct; any reasonable compiler knows how to optimize > side-effect-free expressions like these. (The reverse > transformation, from the arithmetic expression to the boolean one, > is actually harder for the compiler in general.) > > Second, the overwhelming precedent in FreeBSD is to use boolean > operators to combine boolean expressions, so you might try to get > some consensus on the issue before you go around replacing them > with bitwise operators. I for one don't find the bitwise > operators clearer, but I don't speak for everyone else. I concur, it should just use boolean logic since it is doing a boolean test. -- John Baldwin
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