f0d1b0b30d
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>
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| .. | ||
| raid6test | ||
| .gitignore | ||
| bitmap.c | ||
| dm-bio-list.h | ||
| dm-bio-record.h | ||
| dm-crypt.c | ||
| dm-emc.c | ||
| dm-exception-store.c | ||
| dm-hw-handler.c | ||
| dm-hw-handler.h | ||
| dm-io.c | ||
| dm-io.h | ||
| dm-ioctl.c | ||
| dm-linear.c | ||
| dm-log.c | ||
| dm-log.h | ||
| dm-mpath.c | ||
| dm-mpath.h | ||
| dm-path-selector.c | ||
| dm-path-selector.h | ||
| dm-raid1.c | ||
| dm-round-robin.c | ||
| dm-snap.c | ||
| dm-snap.h | ||
| dm-stripe.c | ||
| dm-table.c | ||
| dm-target.c | ||
| dm-zero.c | ||
| dm.c | ||
| dm.h | ||
| faulty.c | ||
| Kconfig | ||
| kcopyd.c | ||
| kcopyd.h | ||
| linear.c | ||
| Makefile | ||
| md.c | ||
| mktables.c | ||
| multipath.c | ||
| raid0.c | ||
| raid1.c | ||
| raid5.c | ||
| raid6.h | ||
| raid6algos.c | ||
| raid6altivec.uc | ||
| raid6int.uc | ||
| raid6mmx.c | ||
| raid6recov.c | ||
| raid6sse1.c | ||
| raid6sse2.c | ||
| raid6x86.h | ||
| raid10.c | ||
| unroll.pl | ||
| xor.c | ||