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Merge 20b781599d into 804110a487

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Zhongxian Pan 2024-04-17 14:58:08 +00:00 committed by GitHub
parent 804110a487 20b781599d
commit d11e9b2378
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1 changed files with 4 additions and 11 deletions
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src/hyperloglog.c
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@ -429,7 +429,7 @@ uint64_t MurmurHash64A (const void * key, int len, unsigned int seed) {
* of the pattern 000..1 of the element hash. As a side effect 'regp' is
* set to the register index this element hashes to. */
int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
uint64_t hash, bit, index;
uint64_t hash, index;
int count;
/* Count the number of zeroes starting from bit HLL_REGISTERS
@ -439,21 +439,14 @@ int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
* Note that the final "1" ending the sequence of zeroes must be
* included in the count, so if we find "001" the count is 3, and
* the smallest count possible is no zeroes at all, just a 1 bit
* at the first position, that is a count of 1.
*
* This may sound like inefficient, but actually in the average case
* there are high probabilities to find a 1 after a few iterations. */
* at the first position, that is a count of 1. */
hash = MurmurHash64A(ele,elesize,0xadc83b19ULL);
index = hash & HLL_P_MASK; /* Register index. */
hash >>= HLL_P; /* Remove bits used to address the register. */
hash |= ((uint64_t)1<<HLL_Q); /* Make sure the loop terminates
and count will be <= Q+1. */
bit = 1;
count = 1; /* Initialized to 1 since we count the "00000...1" pattern. */
while((hash & bit) == 0) {
count++;
bit <<= 1;
}
count = __builtin_ctzll(hash) + 1;
*regp = (int) index;
return count;
}