Clean, efficient algorithm for wrapping integers in C++

Question

/**
  * Returns a number between kLowerBound and kUpperBound
  * e.g.: Wrap(-1, 0, 4); // Returns 4
  * e.g.: Wrap(5, 0, 4); // Returns 0      
  */
int Wrap(int con         


        

Answer 1

Actually, since -1 % 4 returns -1 on every system I've even been on, the simple mod solution doesn't work. I would try:

int range = kUpperBound  - kLowerBound +1;
kx = ((kx - kLowerBound) % range) + range;
return (kx % range) + kLowerBound;

if kx is positive, you mod, add range, and mod back, undoing the add. If kx is negative, you mod, add range which makes it positive, then mod again, which doesn't do anything.