lkml.org 
[lkml]   [2008]   [Feb]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] Avoid divides in BITS_TO_LONGS
BITS_PER_LONG is a signed value (32 or 64)

DIV_ROUND_UP(nr, BITS_PER_LONG) performs signed arithmetic if "nr" is signed too.

Converting BITS_TO_LONGS(nr) to DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
makes sure compiler can perform a right shift, even if "nr" is a signed value,
instead of an expensive integer divide.

Applying this patch saves 141 bytes on x86 when CONFIG_CC_OPTIMIZE_FOR_SIZE=y
and speedup bitmap operations.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 69c1edb..be5c27c 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -6,8 +6,8 @@
#define BIT(nr) (1UL << (nr))
#define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG))
#define BIT_WORD(nr) ((nr) / BITS_PER_LONG)
-#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_LONG)
#define BITS_PER_BYTE 8
+#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
#endif

/*
\
 
 \ /
  Last update: 2008-02-07 08:57    [W:0.027 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site