暴雪stringHash

/*********************************StringHash.h*********************************/

#pragma once

#define MAXTABLELEN 1024 // 默认哈希索引表大小
//////////////////////////////////////////////////////////////////////////
// 哈希索引表定义
typedef struct _HASHTABLE
{
long nHashA;
long nHashB;
bool bExists;
}HASHTABLE, *PHASHTABLE ;

class StringHash
{
public:
StringHash(const long nTableLength = MAXTABLELEN);
~StringHash(void);
private:
unsigned long cryptTable[0x500];
unsigned long m_tablelength; // 哈希索引表长度
HASHTABLE *m_HashIndexTable;
private:
void InitCryptTable(); // 对哈希索引表预处理
unsigned long HashString(const string& lpszString, unsigned long dwHashType); // 求取哈希值
public:
bool Hash(string url);
unsigned long Hashed(string url); // 检测url是否被hash过
};



/*********************************StringHash.cpp*********************************/

#include "StdAfx.h"
#include "StringHash.h"

StringHash::StringHash(const long nTableLength /*= MAXTABLELEN*/)
{
InitCryptTable();
m_tablelength = nTableLength;
//初始化hash表
m_HashIndexTable = new HASHTABLE[nTableLength];
for ( int i = 0; i < nTableLength; i++ )
{
m_HashIndexTable[i].nHashA = -1;
m_HashIndexTable[i].nHashB = -1;
m_HashIndexTable[i].bExists = false;
}
}

StringHash::~StringHash(void)
{
//清理内存
if ( NULL != m_HashIndexTable )
{
delete []m_HashIndexTable;
m_HashIndexTable = NULL;
m_tablelength = 0;
}
}

/************************************************************************/
/*函数名：InitCryptTable
/*功 能：对哈希索引表预处理
/*返回值：无
/************************************************************************/
void StringHash::InitCryptTable()
{
unsigned long seed = 0x00100001, index1 = 0, index2 = 0, i;

for( index1 = 0; index1 < 0x100; index1++ )
{
for( index2 = index1, i = 0; i < 5; i++, index2 += 0x100 )
{
unsigned long temp1, temp2;
seed = (seed * 125 + 3) % 0x2AAAAB;
temp1 = (seed & 0xFFFF) << 0x10;
seed = (seed * 125 + 3) % 0x2AAAAB;
temp2 = (seed & 0xFFFF);
cryptTable[index2] = ( temp1 | temp2 );
}
}
}

/************************************************************************/
/*函数名：HashString
/*功 能：求取哈希值
/*返回值：返回hash值
/************************************************************************/
unsigned long StringHash::HashString(const string& lpszString, unsign

ed long dwHashType)
{
unsigned char *key = (unsigned char *)(const_cast(lpszString.c_str()));
unsigned long seed1 = 0x7FED7FED, seed2 = 0xEEEEEEEE;
int ch;

while(*key != 0)
{
ch = toupper(*key++);

seed1 = cryptTable[(dwHashType << 8) + ch] ^ (seed1 + seed2);
seed2 = ch + seed1 + seed2 + (seed2 << 5) + 3;
}
return seed1;
}

/************************************************************************/
/*函数名：Hashed
/*功 能：检测一个字符串是否被hash过
/*返回值：如果存在，返回位置；否则，返回-1
/************************************************************************/
unsigned long StringHash::Hashed(string lpszString)

{
const unsigned long HASH_OFFSET = 0, HASH_A = 1, HASH_B = 2;
//不同的字符串三次hash还会碰撞的几率无限接近于不可能
unsigned long nHash = HashString(lpszString, HASH_OFFSET);
unsigned long nHashA = HashString(lpszString, HASH_A);
unsigned long nHashB = HashString(lpszString, HASH_B);
unsigned long nHashStart = nHash % m_tablelength,
nHashPos = nHashStart;

while ( m_HashIndexTable[nHashPos].bExists)
{
if (m_HashIndexTable[nHashPos].nHashA == nHashA && m_HashIndexTable[nHashPos].nHashB == nHashB)
return nHashPos;
else
nHashPos = (nHashPos + 1) % m_tablelength;

if (nHashPos == nHashStart)
break;
}

return -1; //没有找到
}

/************************************************************************/
/*函数名：Hash
/*功 能：hash一个字符串
/*返回值：成功，返回true；失败，返回false
/************************************************************************/
bool StringHash::Hash(string lpszString)
{
const unsigned long HASH_OFFSET = 0, HASH_A = 1, HASH_B = 2;
unsigned long nHash = HashString(lpszString, HASH_OFFSET);
unsigned long nHashA = HashString(lpszString, HASH_A);
unsigned long nHashB = HashString(lpszString, HASH_B);
unsigned long nHashStart = nHash % m_tablelength,
nHashPos = nHashStart;

while ( m_HashIndexTable[nHashPos].bExists)
{
nHashPos = (nHashPos + 1) % m_tablelength;
if (nHashPos == nHashStart) //一个轮回
{
//hash表中没有空余的位置了,无法完成hash
return false;
}
}
m_HashIndexTable[nHashPos].bExists = true;
m_HashIndexTable[nHashPos].nHashA = nHashA;
m_HashIndexTable[nHashPos].nHashB = nHashB;

return true;
}