关于float /double、string类型的hash函数/hash表实现(转)

#include <ext/hash_map>
#include <math.h>
#include <stdio.h>
using namespace std;

#define FLT_EPSILON 1.192093e-007
#define DBL_EPSILON 2.2204460492503131e-016
#define FLOAT_EPSILON(a,b) ( a > b ? fabs(a) * FLT_EPSILON : fabs(b) * FLT_EPSILON)
#define DOUBLE_EPSILON(a,b) ( a > b ? fabs(a) * FLT_EPSILON : fabs(b) * DBL_EPSILON)
#define float_equal(a, b) (fabs((a)-(b)) <= FLOAT_EPSILON(a,b))
#define double_equal(a, b) (fabs((a)-(b)) <= DOUBLE_EPSILON(a,b))
#define INT64_MAX 0x7fffffffffffffffLL

typedef struct
{
    size_t operator()(const double & dValue) const
    {
        int e =  ;
        double tmp = dValue;
        if (dValue<)
        {
            tmp = -dValue;
        }
        e = ceil (log (dValue));
        return size_t(( INT64_MAX+ 1.0) * tmp * exp (-e));
    }
} hash_double; 

typedef struct
{
    bool operator()(const double &value1,const double &value2) const
    {
        return double_equal(value1,value2);
    }
} hash_double_cmp;  

typedef struct
{
    size_t operator()(const string & str) const
    {
        size_t h=;for(size_t i=;i<str.length();++i)
        {
            h = ( h<< ) - h + str[i];
        }
        return h;
        //return __stl_hash_string(str.c_str());
    }
} hash_string;  

typedef struct
{
    bool operator()(const string &str1,const string &str2) const
    {
        return str1.compare(str2) == ;
    }
} hash_str_cmp;  

http://blog.csdn.net/templarzq/article/details/7702910