/* * hyperloglog.h * * A simple HyperLogLog cardinality estimator implementation * * Portions Copyright (c) 2014-2021, 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 * * 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 */