Method divide

output/java_guava/1.4.19/IntMath.java:323–379

Returns the result of dividing p by q, rounding using the specified RoundingMode. @throws ArithmeticException if q == 0, or if mode == UNNECESSARY and a is not an integer multiple of b

(int p, int q, RoundingMode mode)

   */

  @SuppressWarnings("fallthrough")
  public static int divide(int p, int q, RoundingMode mode) {
    checkNotNull(mode);
    if (q == 0) {
      throw new ArithmeticException("/ by zero"); // for GWT
    }

    int div = p / q;
    int rem = p - q * div; // equal to p % q
    if (rem == 0) {
      return div;
    }

    /*
     * Normal Java division rounds towards 0, consistently with RoundingMode.DOWN. We just have to
     * deal with the cases where rounding towards 0 is wrong, which typically depends on the sign of
     * p / q.
     *
     * signum is 1 if p and q are both nonnegative or both negative, and -1 otherwise.
     */

    int signum = 1 | ((p ^ q) >> (Integer.SIZE - 1));
    boolean increment;
    switch (mode) {
      case UNNECESSARY:
        checkRoundingUnnecessary(rem == 0);
        // fall through
      case DOWN:
        increment = false;
        break;
      case UP:
        increment = true;
        break;
      case CEILING:
        increment = signum > 0;
        break;
      case FLOOR:
        increment = signum < 0;
        break;
      case HALF_EVEN:
      case HALF_DOWN:
      case HALF_UP:
        int absRem = abs(rem);
        int cmpRemToHalfDivisor = absRem - (abs(q) - absRem);
        // subtracting two nonnegative ints can't overflow
        // cmpRemToHalfDivisor has the same sign as compare(abs(rem), abs(q) / 2).
      if (cmpRemToHalfDivisor == 0) { // exactly on the half mark
        increment = (mode == HALF_UP || (mode == HALF_EVEN & (div & 1) != 0));
      } else {
        increment = cmpRemToHalfDivisor > 0; // closer to the UP value
      }
      break;
      default:
        throw new AssertionError();
    }
    return increment ? div + signum : div;
  }