| /* | |
| * hyperloglog.h | |
| * | |
| * A simple HyperLogLog cardinality estimator implementation | |
| * | |
| * Portions Copyright (c) 2014-2024, 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. | |
| */ | |
| /* | |
| * 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); | |