TarsCpp/util/include/util/tc_hash_fun.h

/**
 * Tencent is pleased to support the open source community by making Tars available.
 *
 * Copyright (C) 2016THL A29 Limited, a Tencent company. All rights reserved.
 *
 * Licensed under the BSD 3-Clause License (the "License"); you may not use this file except 
 * in compliance with the License. You may obtain a copy of the License at
 *
 * https://opensource.org/licenses/BSD-3-Clause
 *
 * Unless required by applicable law or agreed to in writing, software distributed 
 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
 * CONDITIONS OF ANY KIND, either express or implied. See the License for the 
 * specific language governing permissions and limitations under the License.
 */

#ifndef _TC_HASH_FUN_H_
#define _TC_HASH_FUN_H_

#include <iostream>
#include <string>

using namespace std;

namespace tars
{
/////////////////////////////////////////////////
/** 
 * @file tc_hash_fun.h 
 * @brief hash算法.
 *可以对输入的字节流进行hash得到相当均匀的hash值 
 *  
 *
 */             
/////////////////////////////////////////////////

template <class _Key> struct hash { };
template <class _Key> struct hash_new { };

inline size_t hash_string(const char* s)
{
    unsigned long h = 0; 
    for ( ; *s; ++s)
    h = 5*h + *s;

    return size_t(h);
}

//////////////////////////////////////////////////////////
/**
 * @brief 尽量采用hash_new, 更均衡一些.
 *  
 *可以对输入的字节流进行hash得到相当均匀的hash值
 */
//////////////////////////////////////////////////////////
template <>
struct hash<string>
{
    size_t operator()(const string &s) const
    {
        size_t h = 0, g;
        const char *arKey = s.c_str();
        size_t nKeyLength = s.length();
        const char *arEnd = arKey + nKeyLength;
        while (arKey < arEnd)
        {
            h = (h << 4) + *arKey++;
            if ((g = (h & 0xF0000000)))
            {
                h = h ^ (g >> 24);
                h = h ^ g;
            }
        }
        return h;
    }
};

template <>
struct hash_new<string>
{
    size_t operator()(const string &s) const
    {
        const char *ptr= s.c_str();
        size_t key_length = s.length();
        uint32_t value= 0;
        
        while (key_length--) 
        {
            value += *ptr++;
            value += (value << 10);
            value ^= (value >> 6);
        }
        value += (value << 3);
        value ^= (value >> 11);
        value += (value << 15); 
        
        return value == 0 ? 1 : value;
    }
};

template <>
struct hash<char*>
{ 
    size_t operator()(const char* s) const { return hash_string(s); }
};

template <>
struct hash<const char*>
{ 
    size_t operator()(const char* s) const { return hash_string(s); }
};

template <>
struct hash<char> 
{ 
    size_t operator()(char x) const { return x; }
};

template <>
struct hash<unsigned char> 
{ 
    size_t operator()(unsigned char x) const { return x; }
};

template <>
struct hash<signed char> 
{ 
    size_t operator()(unsigned char x) const { return x; }
};

template <>
struct hash<short> 
{ 
    size_t operator()(short x) const { return x; }
};

template <>
struct hash<unsigned short> 
{ 
    size_t operator()(unsigned short x) const { return x; }
};

template <>
struct hash<int> 
{
    size_t operator()(int x) const { return x; }
};

template <>
struct hash<unsigned int> 
{ 
    size_t operator()(unsigned int x) const { return x; }
};

template <>
struct hash<long> 
{ 
    size_t operator()(long x) const { return x; }
};

template <>
struct hash<unsigned long> 
{ 
    size_t operator()(unsigned long x) const { return x; }
};

/**
* @brief 一个奇妙的hash算法.
*  
*可以对输入的字节流进行hash得到相当均匀的hash值
*/
struct magic_string_hash
{
    size_t operator()(const string &s) const
    {
        const char *ptr= s.c_str();
        size_t key_length = s.length();
        uint32_t value= 0;
        
        while (key_length--) 
        {
            value += *ptr++;
            value += (value << 10);
            value ^= (value >> 6);
        }
        value += (value << 3);
        value ^= (value >> 11);
        value += (value << 15); 
        
        return value == 0 ? 1 : value;
    }
};

////////////////////////////////////////////////////////////////////
}

#endif