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author | 2006-12-08 02:37:49 -0800 | |
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committer | 2006-12-08 08:28:51 -0800 | |
commit | f0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8 (patch) | |
tree | 0aa5379150574374351fb92af7881a48dbfcf2ce /arch/x86_64 | |
parent | [PATCH] struct path: convert zorro (diff) | |
download | linux-f0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8.tar.gz linux-f0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8.tar.bz2 linux-f0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8.zip |
[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/x86_64')
-rw-r--r-- | arch/x86_64/Kconfig | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86_64/Kconfig b/arch/x86_64/Kconfig index 3254a616c69e..3ac581d17202 100644 --- a/arch/x86_64/Kconfig +++ b/arch/x86_64/Kconfig @@ -101,6 +101,14 @@ config GENERIC_BUG default y depends on BUG +config ARCH_HAS_ILOG2_U32 + bool + default n + +config ARCH_HAS_ILOG2_U64 + bool + default n + source "init/Kconfig" |