code: public static int floorDiv (int dividend, int divisor) {
          boolean numpos = dividend >= 0, denpos = divisor >= 0;
          if (numpos == denpos) return dividend / divisor;
          return denpos ? (dividend - divisor + 1) / divisor : (dividend - divisor - 1) / divisor;
      }
docs: Computes the floored division {@code dividend/divisor} which is useful when dividing
  potentially negative numbers into bins.
  
  <p> For example, the following numbers {@code floorDiv} 10 are:
  <pre>
  -15 -10 -8 -2 0 2 8 10 15
  -2  -1 -1 -1 0 0 0  1  1
  </pre>