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 id 1cTaPh-000PJF-Ju; Tue, 17 Jan 2017 22:31:29 +0200
Subject: Re: svn commit: r312236 - head/sys/net80211
To: Adrian Chadd <adrian@FreeBSD.org>, Ian Lepore <ian@FreeBSD.org>
References: <201701151949.v0FJnl2h027169@repo.freebsd.org>
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From: Andriy Gapon <avg@FreeBSD.org>
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Date: Tue, 17 Jan 2017 22:30:07 +0200
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On 15/01/2017 22:43, Adrian Chadd wrote:
> On 15 January 2017 at 11:56, Ian Lepore <ian@freebsd.org> wrote:
> 
>>
>> What is the point of the !! in these macros?  The expressions already
>> have boolean type (even in C++ where it matters) due to the ==.
>>  Removing the !! would also make one level of parens redundant.
> 
> It's just a habit i picked up from linux-land. That way it really is
> only 1 or 0, so things like debugging output and such make easier
> sense.

Well, that habit is useful when applied to results of bit-wise operations.
It does nothing but obfuscating the code when applied to results of logical
operations.  Which is the case here.
And even with the bit-wise operation we have a FreeBSD idiom of comparing the
result with zero using != 0.  More verbose, but also more stylish.

> It's also fixed a handful of bugs in the past (but I can't think of
> exact cases right now) - primarily where other code expected 1 or 0
> (for things like shifts into protocol fields) and the macro returns 0
> or ${LARGEVAL}.


-- 
Andriy Gapon