From 2a05fbb94958d3a01370343fc43c963689586985 Mon Sep 17 00:00:00 2001 From: Nate Lawson Date: Tue, 8 Feb 2005 07:51:14 +0000 Subject: [PATCH] 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. --- sys/fs/msdosfs/msdosfs_conv.c | 19 ++++++++++++++----- 1 file 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); } /*