How to golf wrap-around assignments?

This is a relatively simple question. I’m trying to golf a Snake game I’ve written, and I’m trying to work out if there’s a way to golf the following conditional assignments which control x and y coordinates of the snake ensuring a wrap around of the play area:

if (P<0) {
  P = T-1;
}
if (P>T-1) {
  P = 0;
}
if (Q<0) {
  Q = T-1;
}
if (Q>T-1) {
  Q = 0;
}

Is there a simpler way of expressing these, regardless of the value of T?