C++ functions for integer division with well defined rounding strategy

Question

I want something in C++ that lets me do efficient integer division with specified rounding behavior, something like this:

div_down(-4,3)        ==> -2
div_up(         


        

Answer 1

This is what I've got so far, with the precondition d > 0. They all seem to work, but can they be simplified?

int div_down(int n, int d) {
  if (n < 0) {
    return -((d - n - 1) / d);
  } else {
    return n / d;
  }
}

int div_up(int n, int d) {
  if (n < 0) {
    return -(-n / d);
  } else {
    return (n + d - 1) / d;
  }
}

int div_to_zero(int n, int d) {
  return n / d;
}

int div_to_nearest(int n, int d) {
  if (n < 0) {
    return (n - d/2 + 1) / d;
  } else {
    return (n + d/2) / d;
  }
}