linux-kernel - [PATCH 2/7] lib: bitmap: Eliminate branch in __bitmap_shift

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Date:	Fri, 28 Nov 2014 17:01:05 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 2/7] lib: bitmap: Eliminate branch in __bitmap_shift_right

We can shift the bits from lower and upper into place before
assembling dst[k]; moving the shift of upper into the branch where we
already know that rem is non-zero allows us to remove a
conditional.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 lib/bitmap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 2332115..9250c3f 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -127,13 +127,13 @@ void __bitmap_shift_right(unsigned long *dst, const unsigned long *src,
 			upper = src[off + k + 1];
 			if (off + k + 1 == lim - 1 && left)
 				upper &= mask;
+			upper <<= (BITS_PER_LONG - rem);
 		}
 		lower = src[off + k];
 		if (left && off + k == lim - 1)
 			lower &= mask;
-		dst[k] = lower >> rem;
-		if (rem)
-			dst[k] |= upper << (BITS_PER_LONG - rem);
+		lower >>= rem;
+		dst[k] = lower | upper;
 		if (left && k == lim - 1)
 			dst[k] &= mask;
 	}
-- 
2.0.4

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