Re: [PATCH v3 1/7] linux/log2.h: Add roundup/rounddown_pow_two64() family of functions

Robin Murphy
2019-11-27T18:06:31Z

On 26/11/2019 12:51 pm, Leon Romanovsky wrote:
> On Tue, Nov 26, 2019 at 10:19:39AM +0100, Nicolas Saenz Julienne wrote:
>> Some users need to make sure their rounding function accepts and returns
>> 64bit long variables regardless of the architecture. Sadly
>> roundup/rounddown_pow_two() takes and returns unsigned longs. Create a
>> new generic 64bit variant of the function and cleanup rougue custom
>> implementations.
>
> Is it possible to create general roundup/rounddown_pow_two() which will
> work correctly for any type of variables, instead of creating special
> variant for every type?

In fact, that is sort of the case already - roundup_pow_of_two() itself
wraps ilog2() such that the constant case *is* type-independent. And
since ilog2() handles non-constant values anyway, might it be reasonable
to just take the strongly-typed __roundup_pow_of_two() helper out of the
loop as below?

Robin

----->8-----
diff --git a/include/linux/log2.h b/include/linux/log2.h
index 83a4a3ca3e8a..e825f8a6e8b5 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -172,11 +172,8 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
*/
#define roundup_pow_of_two(n) \
( \
- __builtin_constant_p(n) ? ( \
- (n == 1) ? 1 : \
- (1UL << (ilog2((n) - 1) + 1)) \
- ) : \
- __roundup_pow_of_two(n) \
+ (__builtin_constant_p(n) && (n == 1)) ? \
+ 1 : (1UL << (ilog2((n) - 1) + 1)) \
)

/**