unsigned int n = 667;
int* source = (int*)malloc(n);
//filling source
unsigned int k = (n + 7) / 8;
uint8_t* compressed = (uint8_t*)malloc(k);

for (unsigned int i = 0; i < k; ++k)
{
    //???
}

//??? reading last "non-full" byte

//do something

free(compressed);
free(source);