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

Jan Engelhardt
2006-10-09T12:27:56Z

>> > > > 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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