Is using a non-32-bit integer reasonable? [duplicate]

Question

Possible Duplicate:
The importance of using a 16bit integer

If today's processors perform (under standard conditions) 32-bit operations -- then is using a "short int" reasonable? Because in order to perform an operation on that data, it will convert it to a 32-bit (from 16-bit) integer, perform the operations, and then go back to 16-bit -- I think. So what is the point?

In essence my questions are as follows:

1. What (if any) performance gain/hindrance does using a smaller ranged integer bring? Like, if instead of using a standard 32-bit integer for storage, I use a 16-bit short integer.
2. "and then go back to 16-bit" -- Am I correct here? See above.
3. Are all integer data stored as 32-bit integer space on CPU/RAM?

Answer 1

The answer to your first question should also clarify the last one: if you need to store large numbers of 16-bit ints, you save half the amount of memory required for 32-bit ints, with whatever "fringe benefits" that may come along with it, such as using the cache more efficiently.

Most CPUs these days have separate instructions for 16-bit vs. 32-bit operations, along with instructions to read and write 16-bit values from and to memory. Internally, the ALU may be performing a 32-bit operation, but the result for the upper half does not make it back into the registers.