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Unroll the loop for calculating the 8.3 filename checksum. In testing

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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.
This commit is contained in:
Nate Lawson 2005-02-08 07:51:14 +00:00
parent ad6da8a0fc
commit 2a05fbb949
1 changed files with 14 additions and 5 deletions
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19
sys/fs/msdosfs/msdosfs_conv.c
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@ -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);
}
/*