}

func roundShortest(d *decimal, x *Float) {
	// if the mantissa is zero, the number is zero - stop now
	if len(d.mant) == 0 {
		return
	}

	// Approach: All numbers in the interval [x - 1/2ulp, x + 1/2ulp]
	// (possibly exclusive) round to x for the given precision of x.
	// Compute the lower and upper bound in decimal form and find the
	// shortest decimal number d such that lower <= d <= upper.

    }
  }

  @GwtIncompatible // #trueLog2, Math.ulp
  public void testLog2Accuracy() {
    for (double d : POSITIVE_FINITE_DOUBLE_CANDIDATES) {
      double dmLog2 = DoubleMath.log2(d);
      double trueLog2 = trueLog2(d);
      assertTrue(Math.abs(dmLog2 - trueLog2) <= Math.ulp(trueLog2));
    }
  }

  public void testLog2SemiMonotonic() {

	// Table 14: Stress Inputs for Conversion to 24-bit Binary, <1/2 ULP
	"5e-20",
	"67e+14",
	"985e+15",
	"7693e-42",
	"55895e-16",
	"996622e-44",
	"7038531e-32",
	"60419369e-46",
	"702990899e-20",
	"6930161142e-48",
	"25933168707e+13",
	"596428896559e+20",

	// Table 15: Stress Inputs for Conversion to 24-bit Binary, >1/2 ULP
	"3e-23",
	"57e+18",
	"789e-35",
	"2539e-18",

   * </ul>
   *
   * <p>The computed result is within 1 ulp of the exact result.
   *
   * <p>If the result of this method will be immediately rounded to an {@code int}, {@link
   * #log2(double, RoundingMode)} is faster.
   */
  public static double log2(double x) {
    return log(x) / LN_2; // surprisingly within 1 ulp according to tests
  }

  /**

   * </ul>
   *
   * <p>The computed result is within 1 ulp of the exact result.
   *
   * <p>If the result of this method will be immediately rounded to an {@code int}, {@link
   * #log2(double, RoundingMode)} is faster.
   */
  public static double log2(double x) {
    return log(x) / LN_2; // surprisingly within 1 ulp according to tests
  }

  /**

		{uint32(42), " 42 ", false},
		{int16(-42), " -42 ", false},
		{uint16(42), " 42 ", false},
		{int64(-42), " -42 ", false},
		{uint64(42), " 42 ", false},
		{uint64(1) << 53, " 9007199254740992 ", false},
		// ulp(1 << 53) > 1 so this loses precision in JS
		// but it is still a representable integer literal.
		{uint64(1)<<53 + 1, " 9007199254740993 ", false},
		{float32(1.0), " 1 ", false},
		{float32(-1.0), " -1 ", false},

//         point of erf(x) is near 0.6174 (i.e., erf(x)=x when x is
//         near 0.6174), and by some experiment, 0.84375 is chosen to
//         guarantee the error is less than one ulp for erf.
//
//      2. For |x| in [0.84375,1.25], let s = |x| - 1, and
//         c = 0.84506291151 rounded to single (24 bits)
//              erf(x)  = sign(x) * (c  + P1(s)/Q1(s))

// and include err.Num = s.
//
// If s is not syntactically well-formed, ParseFloat returns err.Err = ErrSyntax.
//
// If s is syntactically well-formed but is more than 1/2 ULP
// away from the largest floating point number of the given size,
// ParseFloat returns f = ±Inf, err.Err = ErrRange.
//
// ParseFloat recognizes the string "NaN", and the (possibly signed) strings "Inf" and "Infinity"

	if isExact(real(b)) {
		realAlike = alike(real(a), real(b))
	} else {
		// Allow non-exact special cases to have errors in ULP.
		realAlike = veryclose(real(a), real(b))
	}
	if isExact(imag(b)) {
		imagAlike = alike(imag(a), imag(b))
	} else {
		// Allow non-exact special cases to have errors in ULP.
		imagAlike = veryclose(imag(a), imag(b))
	}
	return realAlike && imagAlike
}
func isExact(x float64) bool {

  // calculations are done with 80-bit precision, while double has 64
  // bits.  Therefore, 4 should be enough for ordinary use.
  //
  // See the following article for more details on ULP:
  // http://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/
  static const size_t kMaxUlps = 4;

  // Constructs a FloatingPoint from a raw floating-point number.
  //