How to store a 64 bit integer in two 32 bit integers and convert back again

Question

I\'m pretty sure its just a matter of some bitwise operations, I\'m just not entirely sure of exactly what I should be doing, and all searches return back \"64 bit vs 32 bit

Answer 1

I don't know if this is any better than the union or memcpy solutions, but I had to unpack/pack signed 64bit integers and didn't really want to mask or shift anything, so I ended up simply treating the 64bit value as two 32bit values and assign them directly like so:

#include 
#include 

void repack(int64_t in)
{
    int32_t a, b;

    printf("input:    %016llx\n", (long long int) in);

    a = ((int32_t *) &in)[0];
    b = ((int32_t *) &in)[1];

    printf("unpacked: %08x %08x\n", b, a);

    ((int32_t *) &in)[0] = a;
    ((int32_t *) &in)[1] = b;

    printf("repacked: %016llx\n\n", (long long int) in);
}