From f0d1b0b30d250a07627ad8b9fbbb5c7cc08422e8 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 8 Dec 2006 02:37:49 -0800 Subject: [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 Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Herbert Xu Cc: David Howells Cc: Wojtek Kaniewski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ext2/super.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'fs/ext2') diff --git a/fs/ext2/super.c b/fs/ext2/super.c index 255cef5f7420..6347c2dbdd81 100644 --- a/fs/ext2/super.c +++ b/fs/ext2/super.c @@ -597,8 +597,6 @@ static int ext2_check_descriptors (struct super_block * sb) return 1; } -#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. @@ -834,9 +832,9 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent) sbi->s_sbh = bh; sbi->s_mount_state = le16_to_cpu(es->s_state); sbi->s_addr_per_block_bits = - log2 (EXT2_ADDR_PER_BLOCK(sb)); + ilog2 (EXT2_ADDR_PER_BLOCK(sb)); sbi->s_desc_per_block_bits = - log2 (EXT2_DESC_PER_BLOCK(sb)); + ilog2 (EXT2_DESC_PER_BLOCK(sb)); if (sb->s_magic != EXT2_SUPER_MAGIC) goto cantfind_ext2; -- cgit v1.2.3