948c97958b
New functions initHyperLogLogError() and freeHyperLogLog() simplify using this module from elsewhere. Author: Tomáš Vondra Review: Peter Geoghegan
70 lines
2.6 KiB
C
70 lines
2.6 KiB
C
/*
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* hyperloglog.h
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*
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* A simple HyperLogLog cardinality estimator implementation
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*
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* Portions Copyright (c) 2014-2016, PostgreSQL Global Development Group
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*
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* Based on Hideaki Ohno's C++ implementation. The copyright terms of Ohno's
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* original version (the MIT license) follow.
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*
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* src/include/lib/hyperloglog.h
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*/
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/*
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* Copyright (c) 2013 Hideaki Ohno <hide.o.j55{at}gmail.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the 'Software'), to
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* deal in the Software without restriction, including without limitation the
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* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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* sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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#ifndef HYPERLOGLOG_H
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#define HYPERLOGLOG_H
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/*
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* HyperLogLog is an approximate technique for computing the number of distinct
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* entries in a set. Importantly, it does this by using a fixed amount of
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* memory. See the 2007 paper "HyperLogLog: the analysis of a near-optimal
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* cardinality estimation algorithm" for more.
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*
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* hyperLogLogState
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*
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* registerWidth register width, in bits ("k")
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* nRegisters number of registers
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* alphaMM alpha * m ^ 2 (see initHyperLogLog())
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* hashesArr array of hashes
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* arrSize size of hashesArr
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*/
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typedef struct hyperLogLogState
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{
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uint8 registerWidth;
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Size nRegisters;
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double alphaMM;
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uint8 *hashesArr;
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Size arrSize;
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} hyperLogLogState;
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extern void initHyperLogLog(hyperLogLogState *cState, uint8 bwidth);
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extern void initHyperLogLogError(hyperLogLogState *cState, double error);
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extern void addHyperLogLog(hyperLogLogState *cState, uint32 hash);
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extern double estimateHyperLogLog(hyperLogLogState *cState);
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extern void mergeHyperLogLog(hyperLogLogState *cState, const hyperLogLogState *oState);
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extern void freeHyperLogLog(hyperLogLogState *cState);
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#endif /* HYPERLOGLOG_H */
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