linux/arch/ppc
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
..
4xx_io [POWERPC] ARCH=ppc pt_regs fixes 2006-10-10 11:55:25 +10:00
8xx_io [PATCH] struct path: convert ppc 2006-12-08 08:28:48 -08:00
8260_io WorkQueue: Fix up arch-specific work items where possible 2006-12-05 19:36:26 +00:00
amiga Remove all inclusions of <linux/config.h> 2006-10-04 03:38:54 -04:00
boot [POWERPC] Add files build to .gitignore 2006-12-04 20:41:29 +11:00
configs [POWERPC] update prep_defconfig 2006-09-13 18:30:08 +10:00
kernel [PATCH] use generic BUG for ppc 2006-12-08 08:28:39 -08:00
lib Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
mm [PATCH] mm: use symbolic names instead of indices for zone initialisation 2006-10-11 11:14:14 -07:00
platforms [POWERPC] Compilation fixes for ppc4xx PCI-less configs 2006-12-04 20:39:24 +11:00
syslib [POWERPC] 8xx: Off-by-one fixes to SCC parameter RAM definitions 2006-12-04 20:39:40 +11:00
xmon [POWERPC] PPC: Fix xmon stack frame address in backtrace 2006-09-21 22:55:06 +10:00
.gitignore [POWERPC] Add files build to .gitignore 2006-12-04 20:41:29 +11:00
Kconfig [PATCH] LOG2: Implement a general integer log2 facility in the kernel 2006-12-08 08:28:51 -08:00
Kconfig.debug ppc: Remove CHRP, POWER3 and POWER4 support from arch/ppc 2006-03-28 10:22:10 +11:00
Makefile Merge branch '85xx' of git://git.kernel.org/pub/scm/linux/kernel/git/galak/powerpc 2006-03-28 17:03:19 +11:00