1/*
2 * hyperloglog.h
3 *
4 * A simple HyperLogLog cardinality estimator implementation
5 *
6 * Portions Copyright (c) 2014-2019, PostgreSQL Global Development Group
7 *
8 * Based on Hideaki Ohno's C++ implementation. The copyright terms of Ohno's
9 * original version (the MIT license) follow.
10 *
11 * src/include/lib/hyperloglog.h
12 */
13
14/*
15 * Copyright (c) 2013 Hideaki Ohno <hide.o.j55{at}gmail.com>
16 *
17 * Permission is hereby granted, free of charge, to any person obtaining a copy
18 * of this software and associated documentation files (the 'Software'), to
19 * deal in the Software without restriction, including without limitation the
20 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
21 * sell copies of the Software, and to permit persons to whom the Software is
22 * furnished to do so, subject to the following conditions:
23 *
24 * The above copyright notice and this permission notice shall be included in
25 * all copies or substantial portions of the Software.
26 *
27 * THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
28 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
29 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
30 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
31 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
32 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
33 * IN THE SOFTWARE.
34 */
35
36#ifndef HYPERLOGLOG_H
37#define HYPERLOGLOG_H
38
39/*
40 * HyperLogLog is an approximate technique for computing the number of distinct
41 * entries in a set. Importantly, it does this by using a fixed amount of
42 * memory. See the 2007 paper "HyperLogLog: the analysis of a near-optimal
43 * cardinality estimation algorithm" for more.
44 *
45 * hyperLogLogState
46 *
47 * registerWidth register width, in bits ("k")
48 * nRegisters number of registers
49 * alphaMM alpha * m ^ 2 (see initHyperLogLog())
50 * hashesArr array of hashes
51 * arrSize size of hashesArr
52 */
53typedef struct hyperLogLogState
54{
55 uint8 registerWidth;
56 Size nRegisters;
57 double alphaMM;
58 uint8 *hashesArr;
59 Size arrSize;
60} hyperLogLogState;
61
62extern void initHyperLogLog(hyperLogLogState *cState, uint8 bwidth);
63extern void initHyperLogLogError(hyperLogLogState *cState, double error);
64extern void addHyperLogLog(hyperLogLogState *cState, uint32 hash);
65extern double estimateHyperLogLog(hyperLogLogState *cState);
66extern void freeHyperLogLog(hyperLogLogState *cState);
67
68#endif /* HYPERLOGLOG_H */
69