src/include/lib/hyperloglog.h

   1 /*
   2  * hyperloglog.h
   3  *
   4  * A simple HyperLogLog cardinality estimator implementation
   5  *
   6  * Portions Copyright (c) 2014-2021, 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  */
  53 typedef struct hyperLogLogState
  54 {
  55         uint8           registerWidth;
  56         Size            nRegisters;
  57         double          alphaMM;
  58         uint8      *hashesArr;
  59         Size            arrSize;
  60 } hyperLogLogState;
  61
  62 extern void initHyperLogLog(hyperLogLogState *cState, uint8 bwidth);
  63 extern void initHyperLogLogError(hyperLogLogState *cState, double error);
  64 extern void addHyperLogLog(hyperLogLogState *cState, uint32 hash);
  65 extern double estimateHyperLogLog(hyperLogLogState *cState);
  66 extern void freeHyperLogLog(hyperLogLogState *cState);
  67
  68 #endif                                                  /* HYPERLOGLOG_H */