谷歌稀疏哈希与杂音哈希函数

本文介绍了谷歌稀疏哈希与杂音哈希函数的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 限时删除！！ 如何在谷歌稀疏哈希映射中使用杂音哈希函数？ 请问我可以一步一步地告诉我如何使用杂音散列函数？ 我使用visual c ++。 目前我在google稀疏哈希映射中使用std :: hash哈希函数。 使用std :: hash和murmur hash实现的goole稀疏哈希映射之间是否存在任何性能差异？ 解决方案 sparse_hash_map 模板提供散列函数。我检查了 https://sites.google.com/site/murmurhash/ ;它的接口不同于 std :: hash<> ，所以你需要编写适配器类。下面是一个工作示例（请注意，适配器仅涵盖一些情况）： #include< iostream> #include< sparsehash / sparse_hash_map> 使用google :: sparse_hash_map; //命名空间，其中类默认存在 using namespace std; // 64位平台的64位散列 //从https://sites.google.com/site/murmurhash/复制 uint64_t MurmurHash64A（const void * key，int len，unsigned int seed） { const uint64_t m = 0xc6a4a7935bd1e995; const int r = 47; uint64_t h = seed ^（len * m）; const uint64_t * data =（const uint64_t *）key; const uint64_t * end = data +（len / 8）; while（data！= end） { uint64_t k = * data ++; k * = m; k ^ = k>> R等 k * = m; h ^ = k; h * = m; } const unsigned char * data2 =（const unsigned char *）data; switch（len& 7） { case 7：h ^ = uint64_t（data2 [6]）< 48; 情况6：h ^ = uint64_t（data2 [5]）<< 40; 情况5：h ^ = uint64_t（data2 [4]）<< 32; 情况4：h ^ = uint64_t（data2 [3]）<< 24; 情况3：h ^ = uint64_t（data2 [2]）<< 16; 情况2：h ^ = uint64_t（data2 [1]）<< 8; 案例1：h ^ = uint64_t（data2 [0]）; h * = m; }; h ^ = h>> R等 h * = m; h ^ = h>> R等 return h; } //不带指针的类型的简单哈希适配器模板< typename T> struct MurmurHasher { size_t operator（）（const T& t）const { return MurmurHash64A（& t，sizeof（t），0）; } }; //专业化字符串模板<> struct MurmurHasher< string> { size_t operator（）（const string& t）const { return MurmurHash64A（t.c_str（），t.size（），0）; } }; $ b $结构eqstr { bool operator（）（const char * s1，const char * s2）const { return（s1 == s2 ）|| （s1& s2&& strcmp（s1，s2）== 0）; } }; $ b $ int main（） { sparse_hash_map< const char *，int，MurmurHasher< const char *>，eqstr>个月; 个月[january] = 31; 个月[二月] = 28; 个月[march] = 31; 个月[april] = 30; 个月[可能] = 31; 个月[june] = 30; 个月[7月] = 31; 个月[august] = 31; 个月[september] = 30; 个月[october] = 31; 个月[11月] = 30; 个月[十二月] = 31; cout<< 9月 - ><<个月[九月]<< ENDL; cout<< 4月 - ><<几个月[四月]< ENDL; cout<< june - ><<个月[june]<< ENDL; cout<< 11月 - ><<个月[11月] ENDL; sparse_hash_map< string，int，MurmurHasher< string>>年份; 年[2012] = 366; cout<< 2012 - ><<年[2012] } 性能可能取决于您的数据模式，所以您应该自己做测试。 How to use murmur hash function in google sparse hash map?Could you please give me step by step instructions on how to use murmur hash function?I'm using visual c++.Currently I'm using std::hash hash function in google sparse hash map.Is there any performance difference between the goole sparse hash maps which are implemented using std::hash and murmur hash? 解决方案 You need to provide hash function to sparse_hash_map template. I've checked https://sites.google.com/site/murmurhash/; it's interface is different than std::hash<>, so you'll need to write adapter class. Here's a working example (keep in mind that adapter only covers some cases):#include <iostream>#include <sparsehash/sparse_hash_map>using google::sparse_hash_map; // namespace where class lives by defaultusing namespace std;// 64-bit hash for 64-bit platforms// copied from https://sites.google.com/site/murmurhash/uint64_t MurmurHash64A ( const void * key, int len, unsigned int seed ){ const uint64_t m = 0xc6a4a7935bd1e995; const int r = 47; uint64_t h = seed ^ (len * m); const uint64_t * data = (const uint64_t *)key; const uint64_t * end = data + (len/8); while(data != end) { uint64_t k = *data++; k *= m; k ^= k >> r; k *= m; h ^= k; h *= m; } const unsigned char * data2 = (const unsigned char*)data; switch(len & 7) { case 7: h ^= uint64_t(data2[6]) << 48; case 6: h ^= uint64_t(data2[5]) << 40; case 5: h ^= uint64_t(data2[4]) << 32; case 4: h ^= uint64_t(data2[3]) << 24; case 3: h ^= uint64_t(data2[2]) << 16; case 2: h ^= uint64_t(data2[1]) << 8; case 1: h ^= uint64_t(data2[0]); h *= m; }; h ^= h >> r; h *= m; h ^= h >> r; return h;}// simple hash adapter for types without pointerstemplate<typename T>struct MurmurHasher { size_t operator()(const T& t) const { return MurmurHash64A(&t, sizeof(t), 0); }};// specialization for stringstemplate<>struct MurmurHasher<string> { size_t operator()(const string& t) const { return MurmurHash64A(t.c_str(), t.size(), 0); }};struct eqstr{ bool operator()(const char* s1, const char* s2) const { return (s1 == s2) || (s1 && s2 && strcmp(s1, s2) == 0); }};int main(){ sparse_hash_map<const char*, int, MurmurHasher<const char*>, eqstr> months; months["january"] = 31; months["february"] = 28; months["march"] = 31; months["april"] = 30; months["may"] = 31; months["june"] = 30; months["july"] = 31; months["august"] = 31; months["september"] = 30; months["october"] = 31; months["november"] = 30; months["december"] = 31; cout << "september -> " << months["september"] << endl; cout << "april -> " << months["april"] << endl; cout << "june -> " << months["june"] << endl; cout << "november -> " << months["november"] << endl; sparse_hash_map<string, int, MurmurHasher<string>> years; years["2012"] = 366; cout << "2012 -> " << years["2012"] << endl;}Performance will probably depend on your data patterns, so you should do the tests yourself. 这篇关于谷歌稀疏哈希与杂音哈希函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 1403页，肝出来的..