Yinghai Lu wrote:
> Linus Torvalds wrote:
>> On Tue, 30 Jun 2009, Yinghai Lu wrote:
>> ?
>>> +#define round_up(x, y) ({ __typeof__(x) __mask = (y)-1; \
>>> + ((x)+__mask) & ~__mask; })
>>> +#define round_down(x, y) ({ __typeof__(x) __mask = (y)-1; (x) & ~__mask; })
>> Yes, except we might as well simplify it. Do it without the statement
>> expressions, using just a single 'y'. Like this:
>>
>> #define __round_mask(x,y) ((__typeof__(x))((y)-1))
>> #define round_up(x,y) (((x) | __round_mask(x,y))+1)
>> #define round_down(x,y) ((x) & ~__round_mask(x,y))
>>
>> (Yeah, it uses 'x' twice, but the second one is for 'typeof', which
>> doesn't actually cause the value to be evaluated, so it's ok).
>>
>> Now those 'round_xyz()' operations will always return a value of a type
>> that is the same as the type of 'x' except it's gone through the normal C
>> integer promotion rules (ie if 'x' is a smaller type than 'int', then it
>> will be promoted to 'int').
>>
>> Not very well tested, but it _looks_ correct, and uses Peter's trick, and
>> willlet the compiler notice that
>>
>> round_up(x,y)-1
>>
>> is the same thing as
>>
>> x | (y-1)
>>
>> which it _could_ have perhaps figured out before, but now it's way more
>> obvious.
>
> how about x = 0, y = 0x100?
>
also x=0x100000, and y=0x100?
YH
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