linux-kernel - [PATCH] ilog2: improve ilog2 for constant arguments

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Date: Thu, 25 Apr 2024 09:59:28 +0800
From: Eric Lin <ericlinsechs@...il.com>
To: 
Cc: Eric Lin <ericlinsechs@...il.com>,
	Jakub Jelinek <jakub@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ilog2: improve ilog2 for constant arguments

Commit 2f78788b55ba ("ilog2: improve ilog2 for constant arguments")
used __builtin_clzll builtin to avoid generating a lot of code
which interferes badly with GCC inlining heuristics.

Cc: Jakub Jelinek <jakub@...hat.com>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Eric Lin <ericlinsechs@...il.com>
---
 tools/include/linux/log2.h | 78 ++++----------------------------------
 1 file changed, 8 insertions(+), 70 deletions(-)

diff --git a/tools/include/linux/log2.h b/tools/include/linux/log2.h
index e20a67d538b8..6180e8f879c4 100644
--- a/tools/include/linux/log2.h
+++ b/tools/include/linux/log2.h
@@ -68,76 +68,14 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
  *
  * selects the appropriately-sized optimised version depending on sizeof(n)
  */
-#define ilog2(n)				\
-(						\
-	__builtin_constant_p(n) ? (		\
-		(n) < 2 ? 0 :			\
-		(n) & (1ULL << 63) ? 63 :	\
-		(n) & (1ULL << 62) ? 62 :	\
-		(n) & (1ULL << 61) ? 61 :	\
-		(n) & (1ULL << 60) ? 60 :	\
-		(n) & (1ULL << 59) ? 59 :	\
-		(n) & (1ULL << 58) ? 58 :	\
-		(n) & (1ULL << 57) ? 57 :	\
-		(n) & (1ULL << 56) ? 56 :	\
-		(n) & (1ULL << 55) ? 55 :	\
-		(n) & (1ULL << 54) ? 54 :	\
-		(n) & (1ULL << 53) ? 53 :	\
-		(n) & (1ULL << 52) ? 52 :	\
-		(n) & (1ULL << 51) ? 51 :	\
-		(n) & (1ULL << 50) ? 50 :	\
-		(n) & (1ULL << 49) ? 49 :	\
-		(n) & (1ULL << 48) ? 48 :	\
-		(n) & (1ULL << 47) ? 47 :	\
-		(n) & (1ULL << 46) ? 46 :	\
-		(n) & (1ULL << 45) ? 45 :	\
-		(n) & (1ULL << 44) ? 44 :	\
-		(n) & (1ULL << 43) ? 43 :	\
-		(n) & (1ULL << 42) ? 42 :	\
-		(n) & (1ULL << 41) ? 41 :	\
-		(n) & (1ULL << 40) ? 40 :	\
-		(n) & (1ULL << 39) ? 39 :	\
-		(n) & (1ULL << 38) ? 38 :	\
-		(n) & (1ULL << 37) ? 37 :	\
-		(n) & (1ULL << 36) ? 36 :	\
-		(n) & (1ULL << 35) ? 35 :	\
-		(n) & (1ULL << 34) ? 34 :	\
-		(n) & (1ULL << 33) ? 33 :	\
-		(n) & (1ULL << 32) ? 32 :	\
-		(n) & (1ULL << 31) ? 31 :	\
-		(n) & (1ULL << 30) ? 30 :	\
-		(n) & (1ULL << 29) ? 29 :	\
-		(n) & (1ULL << 28) ? 28 :	\
-		(n) & (1ULL << 27) ? 27 :	\
-		(n) & (1ULL << 26) ? 26 :	\
-		(n) & (1ULL << 25) ? 25 :	\
-		(n) & (1ULL << 24) ? 24 :	\
-		(n) & (1ULL << 23) ? 23 :	\
-		(n) & (1ULL << 22) ? 22 :	\
-		(n) & (1ULL << 21) ? 21 :	\
-		(n) & (1ULL << 20) ? 20 :	\
-		(n) & (1ULL << 19) ? 19 :	\
-		(n) & (1ULL << 18) ? 18 :	\
-		(n) & (1ULL << 17) ? 17 :	\
-		(n) & (1ULL << 16) ? 16 :	\
-		(n) & (1ULL << 15) ? 15 :	\
-		(n) & (1ULL << 14) ? 14 :	\
-		(n) & (1ULL << 13) ? 13 :	\
-		(n) & (1ULL << 12) ? 12 :	\
-		(n) & (1ULL << 11) ? 11 :	\
-		(n) & (1ULL << 10) ? 10 :	\
-		(n) & (1ULL <<  9) ?  9 :	\
-		(n) & (1ULL <<  8) ?  8 :	\
-		(n) & (1ULL <<  7) ?  7 :	\
-		(n) & (1ULL <<  6) ?  6 :	\
-		(n) & (1ULL <<  5) ?  5 :	\
-		(n) & (1ULL <<  4) ?  4 :	\
-		(n) & (1ULL <<  3) ?  3 :	\
-		(n) & (1ULL <<  2) ?  2 :	\
-		1 ) :				\
-	(sizeof(n) <= 4) ?			\
-	__ilog2_u32(n) :			\
-	__ilog2_u64(n)				\
+#define ilog2(n) \
+( \
+	__builtin_constant_p(n) ?	\
+	((n) < 2 ? 0 :			\
+	 63 - __builtin_clzll(n)) :	\
+	(sizeof(n) <= 4) ?		\
+	__ilog2_u32(n) :		\
+	__ilog2_u64(n)			\
  )
 
 /**
-- 
2.43.0