zeek/src/HyperLogLog.cc

#include <math.h>
#include <stdint.h>
#include "HyperLogLog.h"
#include <iostream>

using namespace std;

  int CardinalityCounter::optimalB(double error){
    double initial_estimate = 2*(log(1.04)-log(error))/log(2);
    int answer = (int) floor(initial_estimate);
    double k;

    do{
      answer++;
      k = pow(2, (answer - initial_estimate)/2);
    }while(erf(k/sqrt(2)) < conf);

    return answer;
  }

   
  CardinalityCounter :: CardinalityCounter(double error_margin){
    int b = optimalB(error_margin);
    m = (uint64_t) pow(2, b);
    buckets = new uint8_t[m];
    
    if(m == 16)
      alpha_m = 0.673;
    else if(m == 32)
      alpha_m = 0.697;
    else if(m == 64)
      alpha_m = 0.709;
    else
      alpha_m = 0.7213/(1+1.079/m);

    for(uint64_t i = 0; i < m; i++){
      buckets[i] = 0;
    }

    V = m;
  }

  CardinalityCounter :: ~CardinalityCounter(){
    delete [] buckets;
    delete &m;
    delete &V;
    delete &alpha_m;
  }

  uint8_t CardinalityCounter :: rank(uint64_t hash_modified){
    uint8_t answer = 0;
    hash_modified = (uint64_t)(hash_modified/m);
    hash_modified *= 2;
    do{
      hash_modified = (uint64_t) (hash_modified/2);
      answer++;
    }while(hash_modified%2 == 0);
    return answer;
  }


 
  void CardinalityCounter::addElement(uint64_t hash){
    uint64_t index = hash % m;
    hash = hash-index;

    if(buckets[index] == 0)
      V--;
    uint8_t temp = rank(hash);
    if(temp > buckets[index]){
      buckets[index] = temp;
    }
  }
  
  double CardinalityCounter::size(){
    double answer = 0;
    for(int i = 0; i < m; i++){
      answer += pow(2, -(int)buckets[i]);
    }
    answer = 1/answer;
    answer = alpha_m*m*m*answer;

    if(answer <= 5*(double)(m/2)){
      return m*log((double) m/V);
    }
    else if(answer <= pow(2,64)/30){
      return answer;
    }
    else{
      return -pow(2,64)*log(1-answer/pow(2,64));
    }
  }

  void CardinalityCounter::merge(CardinalityCounter* c){
    uint8_t* temp = (*c).getBuckets();
    V = 0;
    for(int i = 0; i < m; i++){
      if(temp[i] > buckets[i]){
        buckets[i] = temp[i];
      }
      if(buckets[i] == 0){
        V += 1;
      }
    }
  }

  uint8_t* CardinalityCounter::getBuckets(){
    return buckets;
  }

  uint64_t CardinalityCounter::getM(){
    return m;
  }