linux-kernel - Re: [PATCH 2.6.18-rc4-mm2] Generic boolean

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Date:	Thu, 24 Aug 2006 06:06:06 +0200
From:	Richard Knutsson <ricknu-0@...dent.ltu.se>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
CC:	Andrew Morton <akpm@...l.org>,
	Prajakta Gudadhe <pgudadhe@...dia.com>, jeff@...zik.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.18-rc4-mm2] Generic boolean

Jan Engelhardt wrote:

>Hi,
>
>
>  
>
>>There has been concern about adding other values then 0 and 1. There has been
>>ideas to do something like:
>>bool b = i & 1 : 0;
>>    
>>
>
>I think you miseed a '?'
>  
>
Yes, thanks...

>bool b = (i & 1) ? : 0;
>  
>
...but I meant: bool b = i ? 1 : 0;

>  
>
>>/*or*/
>>bool b = !!i;
>>
>>but all that is needed is just a casting:
>>
>>bool b = (bool) i;
>>    
>>
>
>No casting needed (in fact, casting is more evil than !!). If bool is a
>  
>
Please inform me why casting is evil (other then risking losing data, by 
cutting the value). But also, _Bool-casting is after all a bit special 
since it does not seem (at least by me) to be able to get a wrong value 
(giving it a value other then 0 but reciving 0).

>bool, then the compiler will (hopefully) ensure that b will only get
>values valid for bools.
>  
>
No, not really. Because _Bool is a byte and not a bit, you can put in a 
value other then 0 or 1 if you cast the pointer (if you insert 256 it 
becomes 0). But after all, there should not be any:
if (b == true)
in the code anyway, so it should be ok.

>Jan Engelhardt
>  
>
/Richard Knutsson
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