[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>
diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 580b8a6..b348867 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -1347,8 +1347,6 @@
sb->s_flags = s_flags; /* Restore MS_RDONLY status */
}
-#define log2(n) ffz(~(n))
-
/*
* Maximal file size. There is a direct, and {,double-,triple-}indirect
* block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
@@ -1597,8 +1595,8 @@
sbi->s_desc_per_block = blocksize / sizeof(struct ext3_group_desc);
sbi->s_sbh = bh;
sbi->s_mount_state = le16_to_cpu(es->s_state);
- sbi->s_addr_per_block_bits = log2(EXT3_ADDR_PER_BLOCK(sb));
- sbi->s_desc_per_block_bits = log2(EXT3_DESC_PER_BLOCK(sb));
+ sbi->s_addr_per_block_bits = ilog2(EXT3_ADDR_PER_BLOCK(sb));
+ sbi->s_desc_per_block_bits = ilog2(EXT3_DESC_PER_BLOCK(sb));
for (i=0; i < 4; i++)
sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
sbi->s_def_hash_version = es->s_def_hash_version;