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

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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))	\
  )

 /**



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