#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