Messages in this thread Patch in this message | | | From | Mark Fasheh <> | Subject | [PATCH 22/35] ocfs2: Don't hand-code xor in ocfs2_hamming_encode(). | Date | Thu, 25 Dec 2008 10:04:37 -0800 |
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From: Joel Becker <joel.becker@oracle.com>
When I wrote ocfs2_hamming_encode(), I was following documentation of the algorithm and didn't have quite the (possibly still imperfect) grasp of it I do now. As part of this, I literally hand-coded xor. I would test a bit, and then add that bit via xor to the parity word.
I can, of course, just do a single xor of the parity word and the source word (the code buffer bit offset). This cuts CPU usage by 53% on a mostly populated buffer (an inode containing utmp.h inline).
Joel
Signed-off-by: Joel Becker <joel.becker@oracle.com> Signed-off-by: Mark Fasheh <mfasheh@suse.com> --- fs/ocfs2/blockcheck.c | 67 ++++++++++++++---------------------------------- 1 files changed, 20 insertions(+), 47 deletions(-)
diff --git a/fs/ocfs2/blockcheck.c b/fs/ocfs2/blockcheck.c index 2ce6ae5..1d5083c 100644 --- a/fs/ocfs2/blockcheck.c +++ b/fs/ocfs2/blockcheck.c @@ -31,7 +31,6 @@ #include "blockcheck.h" - /* * We use the following conventions: * @@ -39,26 +38,6 @@ * p = # parity bits * c = # total code bits (d + p) */ -static int calc_parity_bits(unsigned int d) -{ - unsigned int p; - - /* - * Bits required for Single Error Correction is as follows: - * - * d + p + 1 <= 2^p - * - * We're restricting ourselves to 31 bits of parity, that should be - * sufficient. - */ - for (p = 1; p < 32; p++) - { - if ((d + p + 1) <= (1 << p)) - return p; - } - - return 0; -} /* * Calculate the bit offset in the hamming code buffer based on the bit's @@ -109,10 +88,9 @@ static unsigned int calc_code_bit(unsigned int i) */ u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr) { - unsigned int p = calc_parity_bits(nr + d); - unsigned int i, j, b; + unsigned int i, b; - BUG_ON(!p); + BUG_ON(!d); /* * b is the hamming code bit number. Hamming code specifies a @@ -131,27 +109,23 @@ u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr */ b = calc_code_bit(nr + i); - for (j = 0; j < p; j++) - { - /* - * Data bits in the resultant code are checked by - * parity bits that are part of the bit number - * representation. Huh? - * - * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code"> - * In other words, the parity bit at position 2^k - * checks bits in positions having bit k set in - * their binary representation. Conversely, for - * instance, bit 13, i.e. 1101(2), is checked by - * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1. - * </wikipedia> - * - * Note that 'k' is the _code_ bit number. 'b' in - * our loop. - */ - if (b & (1 << j)) - parity ^= (1 << j); - } + /* + * Data bits in the resultant code are checked by + * parity bits that are part of the bit number + * representation. Huh? + * + * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code"> + * In other words, the parity bit at position 2^k + * checks bits in positions having bit k set in + * their binary representation. Conversely, for + * instance, bit 13, i.e. 1101(2), is checked by + * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1. + * </wikipedia> + * + * Note that 'k' is the _code_ bit number. 'b' in + * our loop. + */ + parity ^= b; } /* While the data buffer was treated as little endian, the @@ -174,10 +148,9 @@ u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize) void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr, unsigned int fix) { - unsigned int p = calc_parity_bits(nr + d); unsigned int i, b; - BUG_ON(!p); + BUG_ON(!d); /* * If the bit to fix has an hweight of 1, it's a parity bit. One -- 1.5.6
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