谷歌的变种murmurHash算法

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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));  }}//32bituint32_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;}

//你可以修改参数自己测试下,散列性与且计算很高效！

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