Commit ede9c697 authored Apr 29, 2008 by Eric Dumazet Committed by Linus Torvalds Apr 29, 2008

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent cdac75e6

include/linux/bitops.h

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -6,8 +6,8 @@
	#define BIT(nr) (1UL << (nr))		#define BIT(nr) (1UL << (nr))
	#define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG))		#define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG))
	#define BIT_WORD(nr) ((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_PER_BYTE 8
			#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
	#endif		#endif

	/*		/*