NaN versus -NaN

#include <cmath>
#include <cstdio>
#include <cfloat>
#include <limits>
#include <iostream>
#include <stdint.h>

int main()
{
  {
    double dfNan = std::numeric_limits<double>::quiet_NaN();
    double dfNegNan = -std::numeric_limits<double>::quiet_NaN();

    uint64_t *nNan = (uint64_t *)&dfNan;
    uint64_t *nNegNan = (uint64_t *)&dfNegNan;
    std::cout << ": " << std::hex << *nNan << "\n";
    std::cout << ": " << std::hex << *nNegNan << "\n";
  }

  {
    float fNan = std::numeric_limits<double>::quiet_NaN();
    float fNegNan = -std::numeric_limits<double>::quiet_NaN();

    uint32_t *nNan = (uint32_t *)&fNan;
    uint32_t *nNegNan = (uint32_t *)&fNegNan;
    std::cout << ": " << std::hex << *nNan << "\n";
    std::cout << ": " << std::hex << *nNegNan << "\n";
  }

  std::cout << "1: " << -std::numeric_limits<double>::quiet_NaN() << "\n";
  std::cout << "2: " << std::hex << (uint64_t)std::numeric_limits<double>::quiet_NaN() << "\n";
  std::cout << "3: " << std::hex << (uint64_t)-std::numeric_limits<double>::quiet_NaN() << "\n";
  std::cout << "4: " << std::hex << (uint32_t)std::numeric_limits<float>::quiet_NaN() << "\n";
  std::cout << "5: " << std::hex << (uint32_t)-std::numeric_limits<float>::quiet_NaN() << "\n";

  std::cout << std::signbit(std::numeric_limits<double>::quiet_NaN()) << "\n";
  std::cout << std::signbit(-std::numeric_limits<double>::quiet_NaN()) << "\n";
  std::cout << std::signbit(std::numeric_limits<float>::quiet_NaN()) << "\n";
  std::cout << std::signbit(-std::numeric_limits<float>::quiet_NaN()) << "\n";

  return 0;

}
/*
g++ -std=c++11 -o nan -g -Wall -Wextra nan.cc && ./nan
: 7ff8000000000000
: fff8000000000000
: 7fc00000
: ffc00000
1: -nan
2: 8000000000000000
3: 8000000000000000
4: 0
5: 0
0
1
0
1
*/