Encode a std::uint64_t into vector of floats

Question

I have to do some dirty trickery and pass a std::uint64_t around an application. Unfortunately I am limited to using a std::vector<float> for that.

To my understanding float is 32-bit on most platforms, so it should be possible to split the 64-bit std::uint64_t into two 32-bit ints, represent those as float put them in the vector and reverse the process at the other end.

How can I do this?

Answer 1

Quick and dirty, but standard compliant if I'm not mistaken:

#include <cassert>
// using assert
#include <cstdint>
// using std::uint64_t
#include <cstring>
// using std::memcpy
#include <vector>

std::vector<float> pack(std::uint64_t value)
{
    static_assert(sizeof(value) >= sizeof(float));
    static_assert(sizeof(value) % sizeof(float) == 0);
    std::vector<float> rtrn(sizeof(value) / sizeof(float));
    std::memcpy(rtrn.data(), &value, sizeof(value));
    return rtrn;
}
std::uint64_t unpack(const std::vector<float>& packed)
{
    std::uint64_t rtrn;
    assert(packed.size() == sizeof(rtrn) / sizeof(float));
    std::memcpy(&rtrn, packed.data(), sizeof(rtrn));
    return rtrn;
}