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/*
* hyperloglog.h
*
* A simple HyperLogLog cardinality estimator implementation
*
* Portions Copyright (c) 2014-2023, PostgreSQL Global Development Group
*
* Based on Hideaki Ohno's C++ implementation. The copyright terms of Ohno's
* original version (the MIT license) follow.
*
* src/include/lib/hyperloglog.h
*/
/*
* Copyright (c) 2013 Hideaki Ohno <hide.o.j55{at}gmail.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the 'Software'), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#ifndef HYPERLOGLOG_H
#define HYPERLOGLOG_H
/*
* HyperLogLog is an approximate technique for computing the number of distinct
* entries in a set. Importantly, it does this by using a fixed amount of
* memory. See the 2007 paper "HyperLogLog: the analysis of a near-optimal
* cardinality estimation algorithm" for more.
*
* hyperLogLogState
*
* registerWidth register width, in bits ("k")
* nRegisters number of registers
* alphaMM alpha * m ^ 2 (see initHyperLogLog())
* hashesArr array of hashes
* arrSize size of hashesArr
*/
typedef struct hyperLogLogState
{
uint8 registerWidth;
Size nRegisters;
double alphaMM;
uint8 *hashesArr;
Size arrSize;
} hyperLogLogState;
extern void initHyperLogLog(hyperLogLogState *cState, uint8 bwidth);
extern void initHyperLogLogError(hyperLogLogState *cState, double error);
extern void addHyperLogLog(hyperLogLogState *cState, uint32 hash);
extern double estimateHyperLogLog(hyperLogLogState *cState);
extern void freeHyperLogLog(hyperLogLogState *cState);
#endif /* HYPERLOGLOG_H */
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