hash_map

Hello everyone,

I have a VERY BIG set of double values that I want to map to intervals
so I thought a clever way to do this was using a hash table. Let's say
that I want to map all double values in the range 0-0.5 to a single
std::pair<double,double>.

This is what I've done so far:

#include <iostream>
#include <ext/hash_map>
#include <boost/functional/hash.hpp>

using namespace __gnu_cxx;
using namespace std;

struct eqstr
{
  bool operator()(const double& o, const double& p) const
  {
    return (o == p);
  }
};

namespace __gnu_cxx{

template<>
struct hash<double>
{
  size_t operator()(double __x) const
      {
   boost::hash<double> double_hash;
        return double_hash(__x);
      }
};

}

void lookup(const hash_map<double, pair<double,double> , hash<double>,
eqstr>& Map,
            const double number)
{
 hash_map<double, pair<double,double> , hash<double>,
eqstr>::const_iterator it
    = Map.find(number);
  cout << number << ": "
       << (it != Map.end() ? "present" : "not present")
       << endl;
}

int main()
{
  hash_map<double, pair<double,double> , hash<double>, eqstr> HashMap;
  HashMap.insert(make_pair(0.1,make_pair(0.,0.5)));
  lookup(HashMap,0.1);
  lookup(HashMap,0.05);
}

aaragon@aaragon-laptop:~/Desktop$ ./a.out
0.1: present
0.05: not present

Now, the thing is that I can't map the value of 0.05 to the same pair
because my hashing function doesn't to this. Any ideas???

Thank you,

a^2