* Re: [PATCH] reiserfscore/hashes.c
2012-11-06 19:47 ` [PATCH] reiserfscore/hashes.c Edward Shishkin
@ 2012-11-07 0:37 ` Michael W. Bombardieri
2012-11-07 14:39 ` Edward Shishkin
2012-11-14 23:38 ` Jeff Mahoney
1 sibling, 1 reply; 4+ messages in thread
From: Michael W. Bombardieri @ 2012-11-07 0:37 UTC (permalink / raw)
To: Edward Shishkin; +Cc: reiserfs-devel, Jeff Mahoney
On Tue, Nov 06, 2012 at 08:47:27PM +0100, Edward Shishkin wrote:
> 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.
I agree. Something doesn't look right about the nested loops
not being entered. This could well point to the code being
incorrect. IMHO, the developer would not bother adding the
loops if he didn't want them to be used.
> Generally I think that this hash is not heavily used: everyone uses either
> r5, or tea hash, so...
I suppose this would raise the question, is it worth patching
yura_hash() or is it better to scrap the function altogether
if the two other hash functions are sufficient?
> A??ked-by: Edward Shishkin <edward.shishkin@gmail.com>
>
> 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;
> > }
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] reiserfscore/hashes.c
2012-11-06 19:47 ` [PATCH] reiserfscore/hashes.c Edward Shishkin
2012-11-07 0:37 ` Michael W. Bombardieri
@ 2012-11-14 23:38 ` Jeff Mahoney
1 sibling, 0 replies; 4+ messages in thread
From: Jeff Mahoney @ 2012-11-14 23:38 UTC (permalink / raw)
To: Edward Shishkin; +Cc: Michael W. Bombardieri, reiserfs-devel, Jeff Mahoney
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On 11/6/12 2:47 PM, Edward Shishkin wrote:
> 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:
Hi Michael -
Can you send the patch directly to me (or the list) so I can just git
am it? It should have a subject like [PATCH] reiserfscore: clarify
yura_hash or something.
- -Jeff
>> 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@gmail.com>
>
> 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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- --
Jeff Mahoney
SUSE Labs
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^ permalink raw reply [flat|nested] 4+ messages in thread