linux-kernel - Re: [PATCH 1/4] LOG2: Implement a general integer log2 facility in the kernel [try #4]

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Message-ID: <Pine.LNX.4.61.0610091416290.4279@yvahk01.tjqt.qr>
Date:	Mon, 9 Oct 2006 14:20:26 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Kyle Moffett <mrmacman_g4@....com>
cc:	David Howells <dhowells@...hat.com>,
	Matthew Wilcox <matthew@....cx>, torvalds@...l.org,
	akpm@...l.org, sfr@...b.auug.org.au, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/4] LOG2: Implement a general integer log2 facility in
 the kernel [try #4]

>> > > > Were you planning on porting Linux to a machine with
>> > > > non-8-bit-bytes any
>> > > > time soon?  Because there's a lot more to fix than this.
>> > > 
>> > > I am considering the case [assuming 8-bit-byte machines] where
>> > > sizeof(u32) is not 4. Though I suppose GCC will probably make a
>> > > 32-bit
>> > > type up if the hardware does not know one.
>> > 
>> > If the machine has 8-bit bytes, how can sizeof(u32) be anything other
>> > than 4?
>> 
>> typedef unsigned int u32;
>> 
>> Though this should not be seen in the linux kernel.
>
> Well, uhh, actually...
>
> All presently-supported architectures do exactly that.  Well, some do:
>
> typedef unsigned int __u32;
> #ifdef __KERNEL__
> typedef __u32 u32;
> #endif

Ouch ouch ouch. It should better be

typedef uint32_t __u32;

So that even if there happens to be a compiler that does sizeof(int)=8,
sizeof(u32) will actually be 4. Say, if there happens to be an
architecture that does only know 64-bit integers, the compiler will
have some extra magic to make uint32_t behave like a 32-bit type in C
and transparently use 64-bit assembler. So far the theory.


	-`J'
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