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| author | Nate Lawson <njl@FreeBSD.org> | 2005-02-08 07:51:14 +0000 |
|---|---|---|
| committer | Nate Lawson <njl@FreeBSD.org> | 2005-02-08 07:51:14 +0000 |
| commit | 2a05fbb94958d3a01370343fc43c963689586985 (patch) | |
| tree | 2fbbc4495c2801ec899b03762583284d83d706df | |
| parent | ad6da8a0fc3cea2fb0b9760b44815d22f0a0fdf6 (diff) | |
| download | src-2a05fbb94958d3a01370343fc43c963689586985.tar.gz src-2a05fbb94958d3a01370343fc43c963689586985.zip | |
Unroll the loop for calculating the 8.3 filename checksum. In testing
on my P3, microbenchmarks show the unrolled version is 78x faster. In
actual use (recursive ls), this gives an average of 9% improvement in
system time and 2% improvement in wall time.
Notes
Notes:
svn path=/head/; revision=141497
| -rw-r--r-- | sys/fs/msdosfs/msdosfs_conv.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/sys/fs/msdosfs/msdosfs_conv.c b/sys/fs/msdosfs/msdosfs_conv.c index 72439e41d412..1f4a32e345b1 100644 --- a/sys/fs/msdosfs/msdosfs_conv.c +++ b/sys/fs/msdosfs/msdosfs_conv.c @@ -909,18 +909,27 @@ win2unixfn(wep, chksum, pmp) } /* - * Compute the checksum of a DOS filename for Win95 use + * Compute the unrolled checksum of a DOS filename for Win95 LFN use. */ u_int8_t winChksum(name) u_int8_t *name; { - int i; u_int8_t s; - for (s = 0, i = 11; --i >= 0; s += *name++) - s = (s << 7)|(s >> 1); - return s; + s = name[0]; + s = ((s << 7) | (s >> 1)) + name[1]; + s = ((s << 7) | (s >> 1)) + name[2]; + s = ((s << 7) | (s >> 1)) + name[3]; + s = ((s << 7) | (s >> 1)) + name[4]; + s = ((s << 7) | (s >> 1)) + name[5]; + s = ((s << 7) | (s >> 1)) + name[6]; + s = ((s << 7) | (s >> 1)) + name[7]; + s = ((s << 7) | (s >> 1)) + name[8]; + s = ((s << 7) | (s >> 1)) + name[9]; + s = ((s << 7) | (s >> 1)) + name[10]; + + return (s); } /* |