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Use llroundl() before converting loglog-beta output to integer.

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Otherwise for small cardinalities the algorithm will output something
like, for example, 4.99 for a candinality of 5, that will be converted
to 4 producing a huge error.
This commit is contained in:
antirez 2016-12-16 10:58:19 +01:00
parent 47dea01c85
commit 0224be8811
1 changed files with 4 additions and 4 deletions
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8
src/hyperloglog.c
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@ -993,9 +993,9 @@ uint64_t hllCount(struct hllhdr *hdr, int *invalid) {
} else {
serverPanic("Unknown HyperLogLog encoding in hllCount()");
}
if(server.hll_use_loglogbeta) {
/* For loglog-beta there is a single formula to compute
/* For loglog-beta there is a single formula to compute
* cardinality for the enture range
*/
@ -1008,8 +1008,8 @@ uint64_t hllCount(struct hllhdr *hdr, int *invalid) {
0.03738027*pow(zl,5) +
-0.005384159*pow(zl,6) +
0.00042419*pow(zl,7);
E = alpha*m*(m-ez)*(1/(E+beta));
E = llroundl(alpha*m*(m-ez)*(1/(E+beta)));
} else {
/* Muliply the inverse of E for alpha_m * m^2 to have the raw estimate. */
E = (1/E)*alpha*m*m;