/// <summary>
/// Computes the natural logarithm of a double double value.
/// </summary>
/// <param name="x">The argument of the logarithm.</param>
/// <returns>The value of ln(x).</returns>
public static DoubleDouble Log(DoubleDouble x)
{
double logHi = Math.Log(x.hi);
if (ExtendedMath.IsNotFinite(logHi))
{
return((DoubleDouble)logHi);
}
int e = (int)Math.Round(logHi / Global.LogTwo);
if (e < 0)
{
x *= DoubleDouble.Pow(2.0, -e);
}
else if (e > 0)
{
x /= DoubleDouble.Pow(2.0, e);
}
// At this point 1/\sqrt{2} <= r <= \sqrt{2},
// i.e. 0.707 <= r <= 1.414
x -= DoubleDouble.One;
// Now -0.293 <= r - 1 <= 0.414.
// We have lost some accuracy if r ~ 1, i.e. x was very close
// to an exact power of 2.
return(e * log2 + Log1P(x));
}
/// <summary>
/// Computes the product of two double double numbers.
/// </summary>
/// <param name="x">The first number.</param>
/// <param name="y">The second number.</param>
/// <returns>The product of <paramref name="x"/> and <paramref name="y"/>.</returns>
public static DoubleDouble operator *(DoubleDouble x, DoubleDouble y)
{
ExtendedMath.TwoProduct(x.hi, y.hi, out double p0, out double p1);
if (p0 == 0.0 || ExtendedMath.IsNotFinite(p0))
{
return((DoubleDouble)p0);
}
ExtendedMath.TwoProduct(x.hi, y.lo, out double p2, out double p4);
ExtendedMath.TwoProduct(x.lo, y.hi, out double p3, out double p5);
double p6 = x.lo * y.lo;
ExtendedMath.ThreeSum(p1, p2, p3, out double t1, out double t2);
t2 += p4 + p5 + p6;
ExtendedMath.ThreeSum(p0, t1, t2, out double pHi, out double pLo);
return(new DoubleDouble(pHi, pLo));
/*
* double zHi, zLo;
* ExtendedMath.TwoProduct(a.hi, b.hi, out zHi, out zLo);
* zLo = (zLo + a.hi * b.lo) + a.lo * b.hi;
* //zLo = (a.hi * b.lo + a.lo * b.hi) + zLo;
*
* return new DoubleDouble(zHi, zLo);
*/
}
/// <summary>
/// Computes the sum of two double double numbers.
/// </summary>
/// <param name="x">The first number.</param>
/// <param name="y">The second number.</param>
/// <returns>The value of <paramref name="x"/> + <paramref name="y"/>.</returns>
public static DoubleDouble operator +(DoubleDouble x, DoubleDouble y)
{
// Add high components
ExtendedMath.TwoSum(x.hi, y.hi, out double sHi, out double sLo);
if (ExtendedMath.IsNotFinite(sHi))
{
return((DoubleDouble)sHi);
}
// Add low components
ExtendedMath.TwoSum(x.lo, y.lo, out double tHi, out double tLo);
ExtendedMath.TwoSum(sHi, sLo + tHi, out double vHi, out double vLo);
ExtendedMath.FastTwoSum(vHi, tLo + vLo, out double zHi, out double zLo);
return(new DoubleDouble(zHi, zLo));
}
/// <summary>
/// Computes the quotient of two double double numbers.
/// </summary>
/// <param name="x">The dividend.</param>
/// <param name="y">The divisor.</param>
/// <returns>The value of <paramref name="x"/> / <paramref name="y"/>.</returns>
public static DoubleDouble operator /(DoubleDouble x, DoubleDouble y)
{
double q1 = x.hi / y.hi;
// If leading order result is NaN or infinity or zero, we are done.
// To continue would introduce NaNs even if result is infinite, so this early return is necessary.
if (q1 == 0.0 || ExtendedMath.IsNotFinite(q1))
{
return((DoubleDouble)q1);
}
DoubleDouble r = x - q1 * y;
double q2 = r.hi / y.hi;
r = r - q2 * y;
double q3 = r.hi / y.hi;
double qHi, qLo;
double t1, t2, t3;
ExtendedMath.TwoSum(q1, q2, out t1, out t2);
ExtendedMath.TwoSum(q3, t1, out qHi, out t3);
ExtendedMath.TwoSum(t2, t3, out qLo, out t1);
return(new DoubleDouble(qHi, qLo));
/*
* // Compute an initial approximation by dividing hi parts.
* double qHi = a.hi / b.hi;
*
* // Compute the product of qHi and bHi to full precision.
* // Ideally this would be exactly aHi but it won't be.
* double uHi, uLo;
* ExtendedMath.TwoProduct(qHi, b.hi, out uHi, out uLo);
*
* // Now compute the correction and but it in qLo.
* double qLo = ((((a.hi - uHi) - uLo) + a.lo) - qHi * b.lo) / b.hi;
*
* return new DoubleDouble(qHi, qLo);
*/
}
/// <summary>
/// Computes the square root of a double double value.
/// </summary>
/// <param name="x">The value of which the square root will be computed.</param>
/// <returns>The value of the square root of x.</returns>
public static DoubleDouble Sqrt(DoubleDouble x)
{
if (x.hi == 0.0)
{
return(0.0);
}
double yHi = Math.Sqrt(x.hi);
if (ExtendedMath.IsNotFinite(yHi))
{
return((DoubleDouble)yHi);
}
ExtendedMath.TwoProduct(yHi, yHi, out double uHi, out double uLo);
double yLo = (((x.hi - uHi) - uLo) + x.lo) / (2.0 * yHi);
return(new DoubleDouble(yHi, yLo));
}
/// <summary>
/// Produces a text representation of the double double value using the given format provider.
/// </summary>
/// <param name="format">The format provider.</param>
/// <returns>A text representation of the value.</returns>
private string ToString(IFormatProvider format)
{
// This algorithm doesn't handle infinities, NaNs, and zeros, but writing them is trivial.
if (ExtendedMath.IsNotFinite(hi) || hi == 0.0)
{
return(hi.ToString(format));
}
// Multiply by a power of 10 to put leading digit in the ones place
Debug.Assert(hi != 0.0);
int e = (int)Math.Floor(Math.Log10(Math.Abs(hi)));
DoubleDouble r = Abs(this);
if (e > 0)
{
r /= Pow(ten, e);
}
else if (e < 0)
{
r *= Pow(ten, -e);
}
// If scaling has screwed us up because of overflow, exit. Fix this.
if (Double.IsNaN(r.hi) || Double.IsNaN(r.lo))
{
return("X");
}
// Spit out up to 32 digits
StringBuilder s = new StringBuilder();
int z = 0;
for (int i = 0; i < 32; i++)
{
if (r.hi == 0.0)
{
break;
}
double t = Math.Floor(r.hi); /* If nothing left, we can stop early */
if (t < 0)
{
t = 0.0; /* if we subtract to zero, sometimes the result can be a very tiny negative number that floors to -1 */
}
int d = (int)t;
Debug.Assert((0 <= d) && (d < 10));
s.Append(d);
if (d == 0)
{
z++;
}
else
{
z = 0;
} /* Keep track of number of trailing zeros for later truncation */
r -= t;
r *= ten;
}
// Remove trailing zeros (which are all after the decimal point)
if (z > 0)
{
s.Remove(s.Length - z, z);
}
// Express in scientific notation for large exponents,
// or by filling in zeros for small exponents.
if (e >= 6)
{
if (s.Length > 1)
{
s.Insert(1, '.');
}
s.Append($"E{e}");
}
else if (e >= 0)
{
if (s.Length > e + 1)
{
s.Insert(e + 1, '.');
}
else
{
s.Append("000000", 0, e - s.Length + 1);
}
}
else if (e >= -4)
{
s.Insert(0, "0.00000".Substring(0, 1 - e)); /* StringBuilder.Append has a substring overload, but StringBuilder.Insert doesn't */
}
else
{
if (s.Length > 1)
{
s.Insert(1, '.');
}
s.Append($"E{e}");
}
// Add a negative sign if necessary
if (hi < 0.0)
{
s.Insert(0, '-');
}
return(s.ToString());
}