diff options
| author | David Howells | 2006-12-08 02:37:49 -0800 |
|---|---|---|
| committer | Linus Torvalds | 2006-12-08 08:28:51 -0800 |
| commit | f0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8 (patch) | |
| tree | 0aa5379150574374351fb92af7881a48dbfcf2ce /arch/parisc | |
| parent | b3d7ae5f47a58a9f7b152deeaf7daa1fc558a8f1 (diff) | |
[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>
Diffstat (limited to 'arch/parisc')
| -rw-r--r-- | arch/parisc/Kconfig | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig index d2101237442e..0f9ff618c6d7 100644 --- a/arch/parisc/Kconfig +++ b/arch/parisc/Kconfig @@ -25,6 +25,14 @@ config RWSEM_GENERIC_SPINLOCK config RWSEM_XCHGADD_ALGORITHM bool +config ARCH_HAS_ILOG2_U32 + bool + default n + +config ARCH_HAS_ILOG2_U64 + bool + default n + config GENERIC_FIND_NEXT_BIT bool default y |