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Revert "Adjust the DOH string hash function"

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Changing the hash function breaks some testcases.

It seems there's a latent bug here (I suspect something somewhere in
SWIG depends on the hash iteration order), but I didn't see where and
we can't really have CI continuing to fail.

See #2303.

This reverts commit 5a96a39aa4.
This commit is contained in:
Olly Betts 2022-07-12 10:51:32 +12:00
commit 216c7f72cf
1 changed files with 6 additions and 14 deletions
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20
Source/DOH/string.c
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@ -180,27 +180,19 @@ static int String_hash(DOH *so) {
if (s->hashkey >= 0) {
return s->hashkey;
} else {
/* We use the djb2 hash function: https://theartincode.stanis.me/008-djb2/
*
* One difference is we use initial seed 0. It seems the usual seed value
* is intended to help spread out hash values, which is beneficial if
* linear probing is used but DOH Hash uses a chain of buckets instead, and
* grouped hash values are probably more cache friendly. In tests using
* 0 seems slightly faster anyway.
*/
const char *c = s->str;
char *c = s->str;
unsigned int len = s->len > 50 ? 50 : s->len;
unsigned int h = 0;
unsigned int mlen = len >> 2;
unsigned int i = mlen;
for (; i; --i) {
h = h + (h << 5) + *(c++);
h = h + (h << 5) + *(c++);
h = h + (h << 5) + *(c++);
h = h + (h << 5) + *(c++);
h = (h << 5) + *(c++);
h = (h << 5) + *(c++);
h = (h << 5) + *(c++);
h = (h << 5) + *(c++);
}
for (i = len - (mlen << 2); i; --i) {
h = h + (h << 5) + *(c++);
h = (h << 5) + *(c++);
}
h &= 0x7fffffff;
s->hashkey = (int)h;