从long编码/解码整数

Question

I have following structs:

struct ID
{
   UINT id;         // range from 0 to 10 000 000
   UINT residentNb; // range same as for id (above).
};

struct FullID
{
   ID myID;
   ID systemID;
};

Now, UINT id in above struct ID have specified range in my system. This range is always from min 0 to max 10 000 000. I would like to transform struct FullID to one number, UINT64 for example, and be able to encode/decode data from it - myID and systemID (like in above struct). Is it possible, and what is the best way to do it? Of course 10 000 000 limit can be rounded to some higher value if this is necessary for proper conversions.

Example

UINT64 encodedID;

(...)

FullID fullID = Decode(encodedID);

(...)

encodedID = Encode(fullID);

Answer 1

I suggest using a union to avoid strict aliasing optimization bugs (google for strict aliasing if you do not know what it is).

And then, just use bitmasks and bitshifts to encode/decode. Stay away from bitfields, they are not easy to work with if you want portable code.