say i have some hardware mmio structure, that has two fields for a pointer, hi and lo is it defined behavior in c to: cast my pointer to uintptr_t split it and assign across those two fields and later in another function: bitwise join the two fields in a uintptr_t cast the result back to the original pointer type that i've allocated beforehand since the value representation should be the same after rebuilding the uintptr, and uintptr is defined as surviving roundtrips, i think it's all good?