谷歌的变种murmurHash算法

全栈程序员-站长 • 2022年10月19日上午6:00 • 未分类 • 阅读 0

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谷歌变种murmurHash的编写与测试

#include<iostream>
#include<stdint.h>
#include<cstring>
#include<time.h>
#include<iterator>
#include<vector>
#include<algorithm>
using namespace std;
bool CheckLittleEndin();
uint32_t DecodeFixed32(const char* data);
uint32_t Hash(const char* data,int size,int seed);
int main(){
  const char* data="assdascxasasdz" ;
  vector<uint32_t> data_;
  vector<uint32_t>::iterator iter;
  vector<uint32_t>::iterator temp;
  int size = strlen(data);
  clock_t start = clock();
  for(int i = 1 ;i<1000000; i++){
    data_.push_back(Hash(data,size,i));
  }
  sort(data_.begin(),data_.end());
  for(iter = data_.begin();iter!=data_.end();iter++){
    cout<<*iter<<endl;

}
  temp = unique(data_.begin(),data_.end());
  cout<<"the last is"<<*(--temp);
  clock_t end = clock();
  cout<<endl;
  cout<<double(end-start)<<"ms";
  return 0;
}
bool CheckLittleEndin(){
  int test = 1;
  int temp = (unsigned char) test;

  if(test) return true;
  else return false;

}
uint32_t DecodeFixed32(const char* data){
  int result;
  if(CheckLittleEndin()){
    memcpy(&result,data,sizeof(result));
  }
  else{
    return ((static_cast<uint32_t>(static_cast<unsigned char>(data[0])))
         | (static_cast<uint32_t>(static_cast<unsigned char>(data[1])) << 8)
         | (static_cast<uint32_t>(static_cast<unsigned char>(data[2])) << 16)
         | (static_cast<uint32_t>(static_cast<unsigned char>(data[3])) << 24));
  }
}
//32bit
uint32_t Hash(const char* data, int size ,int seed){
  const uint32_t r = 24;
  const int m = 0xc6a4a793;
  const char* limit = data + size;

  uint32_t h = seed^(size*m);

  while(data+4<limit){

    uint32_t w = DecodeFixed32(data);
    data = data+4;

    h += w;  //循环操作;
    h *= m;
    h ^= (h >> 16);

  }
  switch (limit - data) {
    case 3:
      h += static_cast<unsigned char>(data[2]) << 16;
      break;
    case 2:
      h += static_cast<unsigned char>(data[1]) << 8;
      break;
    case 1:
      h += static_cast<unsigned char>(data[0]);
      h *= m;
      h ^= (h >> r);  //仅剩余一字节;
      break;
  }
  return h;
}