David,

You're on the right track by looking at the generated code. You will learn a lot from it.

And more in general:
- Use memory space specific pointers when possible instead of generic pointers
- Use unsigned char (uint8_t) when possible instead of int
- Use bit/bool when possible instead of char/int
- Use do { ... } while (--n) when possible instead of while (n--) { ... }

OTOH, when writing code in C, just write what is efficient for you. And worry about code size or execution time efficiency only when it really matters.