Method sqrt

output/java_guava/1.4.16/BigIntegerMath.java:225–258

Returns the square root of x, rounded with the specified rounding mode. @throws IllegalArgumentException if x < 0 @throws ArithmeticException if mode is RoundingMode#UNNECESSARY and sqrt(x) is not an integer

(BigInteger x, RoundingMode mode)

   */

  @GwtIncompatible // TODO
  @SuppressWarnings("fallthrough")
  public static BigInteger sqrt(BigInteger x, RoundingMode mode) {
    checkNonNegative("x", x);
    if (fitsInLong(x)) {
      return BigInteger.valueOf(LongMath.sqrt(x.longValue(), mode));
    }
    BigInteger sqrtFloor = sqrtFloor(x);
    switch (mode) {
      case UNNECESSARY:
        checkRoundingUnnecessary(sqrtFloor.pow(2).equals(x)); // fall through
      case FLOOR:
      case DOWN:
        return sqrtFloor;
      case CEILING:
      case UP:
        int sqrtFloorInt = sqrtFloor.intValue();
boolean sqrtFloorIsExact = (sqrtFloorInt * sqrtFloorInt == x.intValue()) // fast check mod 2^32
 && sqrtFloor.pow(2).equals(x); // slow exact check
      return sqrtFloorIsExact ? sqrtFloor : sqrtFloor.add(BigInteger.ONE);
      case HALF_DOWN:
      case HALF_UP:
      case HALF_EVEN:
        BigInteger halfSquare = sqrtFloor.pow(2).add(sqrtFloor);
        /*
         * We wish to test whether or not x <= (sqrtFloor + 0.5)^2 = halfSquare + 0.25. Since both x
         * and halfSquare are integers, this is equivalent to testing whether or not x <=
         * halfSquare.
         */
      return (halfSquare.compareTo(x) >= 0) ? sqrtFloor : sqrtFloor.add(BigInteger.ONE);
      default:
        throw new AssertionError();
    }
  }

  @GwtIncompatible // TODO
  private static BigInteger sqrtFloor(BigInteger x) {