linux/arch/xtensa
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
configs [PATCH] xtensa: Architecture support for Tensilica Xtensa Part 8 2005-06-24 00:05:22 -07:00
kernel [PATCH] vmlinux.lds: consolidate initcall sections 2006-10-27 15:34:51 -07:00
lib fix file specification in comments 2006-10-03 23:01:26 +02:00
mm fix file specification in comments 2006-10-03 23:01:26 +02:00
platform-iss [PATCH] const struct tty_operations 2006-10-02 07:57:14 -07:00
Kconfig [PATCH] LOG2: Implement a general integer log2 facility in the kernel 2006-12-08 08:28:51 -08:00
Kconfig.debug [PATCH] xtensa: Architecture support for Tensilica Xtensa Part 1 2005-06-24 00:05:21 -07:00
Makefile kconfig: integrate split config into silentoldconfig 2006-06-09 07:31:30 +02:00