Question

If I have a uint64_t original and two regular four byte ints, (which are signed), I would like to store the value in the two ints and recover the unsigned 64 byte later. This should be possible because we have 64 bits available in both cases. I was thinking something along the lines of:

uint64_t test = 1350640807215539000;
int a = test >> 32; //get top 32 bits
int b = test & 0x00000000FFFFFFFF; //keep bottom 32 bits

uint64_t recover_test = ((a << 32) & b);

but this isn’t giving me back the original value of test…what part am I doing wrong?

Answer 1

Instead of doing a lot of error-prone bit-twiddling you could just use a union:

union
{
    uint64_t u64;
    int32_t s32[2];
} u;

u.u64 = 1350640807215539000ULL;

printf("a = %d\n", u.s32[0]);
printf("b = %d\n", u.s32[1]);