lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

[PATCH] LOG2: Implement a general integer log2 facility in the kernel

Browse Source 
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>
This commit is contained in:
David Howells
2006-12-08 02:37:49 -08:00
committed by Linus Torvalds
parent b3d7ae5f47
commit f0d1b0b30d
36 changed files with 384 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
mm/page_alloc.c
View File

@@ -3244,7 +3244,7 @@ void *__init alloc_large_system_hash(const char *tablename,
if (numentries > max)
numentries = max;
log2qty = long_log2(numentries);
log2qty = ilog2(numentries);
do {
size = bucketsize << log2qty;
@@ -3266,7 +3266,7 @@ void *__init alloc_large_system_hash(const char *tablename,
printk("%s hash table entries: %d (order: %d, %lu bytes)\n",
tablename,
(1U << log2qty),
long_log2(size) - PAGE_SHIFT,
ilog2(size) - PAGE_SHIFT,
size);
if (_hash_shift)