linux/arch/arm26
David Howells f0d1b0b30d [PATCH] LOG2: Implement a general integer log2 facility in the kernel
This facility provides three entry points:

	ilog2()		Log base 2 of unsigned long
	ilog2_u32()	Log base 2 of u32
	ilog2_u64()	Log base 2 of u64

These facilities can either be used inside functions on dynamic data:

	int do_something(long q)
	{
		...;
		y = ilog2(x)
		...;
	}

Or can be used to statically initialise global variables with constant values:

	unsigned n = ilog2(27);

When performing static initialisation, the compiler will report "error:
initializer element is not constant" if asked to take a log of zero or of
something not reducible to a constant.  They treat negative numbers as
unsigned.

When not dealing with a constant, they fall back to using fls() which permits
them to use arch-specific log calculation instructions - such as BSR on
x86/x86_64 or SCAN on FRV - if available.

[akpm@osdl.org: MMC fix]
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: David Howells <dhowells@redhat.com>
Cc: Wojtek Kaniewski <wojtekka@toxygen.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-08 08:28:51 -08:00
..
boot Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
kernel [PATCH] arm26: replace kmalloc+memset with kzalloc 2006-12-07 08:39:45 -08:00
lib Remove all inclusions of <linux/config.h> 2006-10-04 03:38:54 -04:00
machine Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
mm [PATCH] slab: remove kmem_cache_t 2006-12-07 08:39:25 -08:00
nwfpe Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
ACKNOWLEDGEMENTS Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
defconfig Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Kconfig [PATCH] LOG2: Implement a general integer log2 facility in the kernel 2006-12-08 08:28:51 -08:00
Kconfig.debug Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Makefile kbuild: change kbuild to not rely on incorrect GNU make behavior 2006-03-06 00:09:51 +01:00