linux-kernel - Re: [KJ][RFC][PATCH] BIT macro cleanup

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Date:	Fri, 23 Feb 2007 12:05:33 -0500
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	"Richard Knutsson" <ricknu-0@...dent.ltu.se>
Cc:	"Milind Choudhary" <milindchoudhary@...il.com>,
	kernel-janitors@...ts.osdl.org, linux-kernel@...r.kernel.org,
	linux-input@...ey.karlin.mff.cuni.cz,
	linux-joystick@...ey.karlin.mff.cuni.cz
Subject: Re: [KJ][RFC][PATCH] BIT macro cleanup

On 2/23/07, Richard Knutsson <ricknu-0@...dent.ltu.se> wrote:
> Dmitry Torokhov wrote:
> > On 2/23/07, Richard Knutsson <ricknu-0@...dent.ltu.se> wrote:
> >> Milind Choudhary wrote:
> >> > On 2/23/07, Richard Knutsson <ricknu-0@...dent.ltu.se> wrote:
> >> >> > +#define BITWRAP(nr)    (1UL << ((nr) % BITS_PER_LONG))
> >> >> >
> >> >> > & make the whole input subsystem use it
> >> >> > The change is huge, more than 125 files using input.h
> >> >> > & almost all use the BIT macro.
> >> >> It is as a big of change, but have you dismissed the "BIT(nr %
> >> >> BITS_PER_LONG)" approach?
> >> >
> >> > no..
> >> > but just looking at the number of places it is being used,
> >> > it seems that adding a new  macro would be good
> >> > which makes it look short n sweet
> >> You have a point there but I still don't think it should be in bitops.h.
> >> Why should we favor long-wrap before byte-wrap, so what do you think
> >> about doing:
> >>
> >> #define BITWRAP(x)      BIT((x) % BITS_PER_LONG)
> >>
> >> in input.h? Otherwise I think it should be call LBITWRAP (or something)
> >> to both show what kind it is and enable us to add others later.
> >
> > Why would you not want to have what you call bitwrap as a standard
> > behavior? Most placed to not use modulus because they know the kind of
> > data they are working with but should still be fine if generic
> > implementation did that.
> >
> Both because I find the name not as expressive as simple "BIT(x %
> something)",

I was not talking about name (I hate BITWRAP) but behavior.

> but mainly since it only enables wrapping of the long-type.

I'd provde BIT and separate LLBIT for ones who really need long long.
People who intereseted in smaller than BITS_PER_LONG bitmaps shoud use
your proposal - BIT(x % DESIRED_WITH) and BIT should do modulo
BITS_PER_LONG internally.

-- 
Dmitry
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