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List:       kernel-janitors
Subject:    Re: Janitor-Question: use __set_bit instead of |=
From:       Jiri Slaby <jirislaby () gmail ! com>
Date:       2011-05-31 9:05:42
Message-ID: 4DE4AF66.8070001 () gmail ! com
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On 05/30/2011 11:23 PM, Peter Hüwe wrote:
> Hi Janitors, staging-list
> 
> what is your opinion on using set_bit instead of using |= to set a bit?
> Is it worth the effort to convert  existing |= to set_bit?
> 
> __set_bit
> pro:
> - often implemented in optimized assembly (e.g. for x86)
> - intention might be clearer
> - less error prone
> - "they are the only portable way to set a specific bit"
> according to  Robert Love's Linux Kernel Development third edition, p.183
> 
> cons:
> uses unsigned longs

Note that you need to define a different set of macros.
E.g. if you have for |=:
#define FLAG1 0x01
#define FLAG2 0x02
#define FLAG3 0x40

for set_bit you need:
#define FLAG1 0
#define FLAG2 1
#define FLAG3 6

Also with set_bit you can set only one bit at a time which might make
the code longer and unreadable. For examples, see input layer.

> |=
> pro:
> - standard C
> - let's the compiler decide
> - no warnings on chars, shorts, ints

regards,
-- 
js
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