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22 lines
531 B
C++
22 lines
531 B
C++
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// This file implements HyperLogLog algorithm, which estimates
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// the number of unique items in a given multiset.
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//
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// For more info, read
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// https://engineering.fb.com/2018/12/13/data-infrastructure/hyperloglog
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#include "mold.h"
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#include <cmath>
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i64 HyperLogLog::get_cardinality() const {
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double z = 0;
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for (i64 val : buckets)
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z += pow(2, -val);
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return ALPHA * NBUCKETS * NBUCKETS / z;
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}
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void HyperLogLog::merge(const HyperLogLog &other) {
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for (i64 i = 0; i < NBUCKETS; i++)
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merge_one(i, other.buckets[i]);
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}
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