On 11/06/2012 04:49 PM, Michael W. Bombardieri wrote:
Hi Edward,
I was browsing the git repository for reiserfs...
https://git.kernel.org/?p=linux/kernel/git/jeffm/reiserfsprogs.git;a=summary
This code is entirely new to me.
I have a patch which simplifies the yura_hash function in
reiserfscore/hashes.c. Here is what it does:
1. Remove temporary variable 'c'
2. Remove two nested loops which always set pow=1
I tested this using the following code on i386 and amd64.
int
main(void)
{
char *test[] = {
"a",
"bb",
"ccc",
"dddd",
"eeeee",
"ffffff",
"ggggggg",
"red leather",
"yellow leather",
NULL
};
size_t n;
int i;
u32 x;
for (i = 0; test[i] != NULL; i++) {
n = strlen(test[i]);
printf("input=\"%s\" len=%u ", test[i], n);
x = yura_hash(test[i], (int)n);
printf("hash=%lu\n", x);
}
return (0);
}
The results between my version and the original
yura_hash are identical:
input="a" len=1 hash=4084352
input="bb" len=2 hash=4148480
input="ccc" len=3 hash=4802688
input="dddd" len=4 hash=11472896
input="eeeee" len=5 hash=79455104
input="ffffff" len=6 hash=772077312
input="ggggggg" len=7 hash=3531332224
input="red leather" len=11 hash=959593472
input="yellow leather" len=14 hash=410631168
I'm not sure if the yura_hash function is used
heavily, or at all. I'm sending this patch in
case you are interested to take a look.
Hello Michael,
Your changes look OK to me.
TBH, I don't like the fact that the pow is set to 1 by such tricky ways in
the mentioned nested loops: it might indicate mistakes in the original
code.
Generally I think that this hash is not heavily used: everyone uses either
r5, or tea hash, so...
Aсked-by: Edward Shishkin <edward.shishkin@xxxxxxxxx>
Thanks,
Edward.
P.S. This is a git repository of Jeff Mahoney, the reiserfs maintainer, so
don't forget cc him ;)
- Michael
--- hashes.c Tue Nov 6 23:21:09 2012
+++ hashes_new.c Tue Nov 6 23:26:26 2012
@@ -175,37 +175,26 @@
u32 yura_hash (const signed char *msg, int len)
{
- int j, pow;
- u32 a, c;
- int i;
-
- for (pow=1,i=1; i < len; i++) pow = pow * 10;
-
- if (len == 1)
- a = msg[0]-48;
- else
- a = (msg[0] - 48) * pow;
-
- for (i=1; i < len; i++) {
- c = msg[i] - 48;
- for (pow=1,j=i; j < len-1; j++) pow = pow * 10;
- a = a + c * pow;
- }
-
- for (; i < 40; i++) {
- c = '0' - 48;
- for (pow=1,j=i; j < len-1; j++) pow = pow * 10;
- a = a + c * pow;
- }
-
- for (; i < 256; i++) {
- c = i;
- for (pow=1,j=i; j < len-1; j++) pow = pow * 10;
- a = a + c * pow;
- }
-
- a = a << 7;
- return a;
+ int i, j, pow;
+ u32 a;
+
+ a = msg[0] - 48;
+ if (len != 1) {
+ for (i = 1, pow = 1; i < len; i++)
+ pow *= 10;
+ a *= pow;
+ }
+ for (i = 1; i < len; i++) {
+ for (j = i, pow = 1; j < len - 1; j++)
+ pow *= 10;
+ a += pow * (msg[i] - 48);
+ }
+ for (; i < 40; i++)
+ a += '0' - 48;
+ for (; i < 256; i++)
+ a += i;
+ a <<= 7;
+ return a;
}
--
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