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

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Date:	Fri, 23 Feb 2007 20:11:15 +0100
From:	Richard Knutsson <ricknu-0@...dent.ltu.se>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
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

Dmitry Torokhov wrote:
> On 2/23/07, Richard Knutsson <ricknu-0@...dent.ltu.se> wrote:
>> Dmitry Torokhov wrote:
>> > I was not talking about name (I hate BITWRAP) but behavior.
>> Oh, my bad :)
>> >
>> >> 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.
>> I agree that _if_ there is a "BITWRAP" then it should be long, but I
>> don't see the reason for it to be in bitops.h when it is only input.h
>> that uses it. + I find it different with BIT since it works as well with
>> 'char' as 'long'.
>> Also, I think it would be best if the name indicated it is a 'long'.
>>
>> Am a little bit curious why you would like it in bitops.h, but won't
>> complain if you do (think you have noticed my view of it ;))
>>
>
> Hm, I thought as was clear, but apparently I messed up explaining my 
> position:
>
> 1. I don't like BITWRAP name at all and I don't want anything like
> that near input code. I think BIT is just fine.
Oh, I think I understand now. So the (in input.h):
#undef BIT
#define BIT(...
business is what you want to do? Well, that I will not object to. Your 
patch with:
+#define BIT(nr)        (1UL << (nr))
+#define LLBIT(nr) (1ULL << (nr))
+#define BITWRAP(nr)    (1UL << ((nr) % BITS_PER_LONG))
in bitops.h made me believe the #undef in input.h was just a temporarily 
thing.
>
> 2. I don't want to use BIT(x % BITS_PER_BITLONG) as it will
> significantly litter code in the input drivers. You want see whta bits
> you are actually setting behind all these "% BITS_PER_BITLONG".
As I said before, I thought it should be defined as BITSWAP (or 
whatever) in input.h and then there is no more "% BITS_PER_LONG" litter. 
But redefining BIT seems like an equally good idea;
+ eas(y/ier) to understand and simple to implement
- another definition of BIT.
>
> 3. I think most of users could use input's implementation of BIT,
> possibly using BIT(x % BM_WIDTH) format to further limit width of the
> bitmap if needed.
Agreed.
>
> 4. LLBIT should be provided to users who really want long long.
Agreed. (As in the case of "BIT(x) (0x800...00ULL >> (x)) )

Richard Knutsson

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