/// <summary>
/// The binary logarithm, log2(x) - for precisions above 1000 bits, use Log() and convert the base.
/// </summary>
private void Log2()
{
if (scratch.Precision.NumBits != mantissa.Precision.NumBits)
{
scratch = new BigInt(mantissa.Precision);
}
int bits = mantissa.Precision.NumBits;
BigFloat temp = new BigFloat(this);
BigFloat result = new BigFloat(exponent, mantissa.Precision);
BigFloat pow2 = new BigFloat(1, mantissa.Precision);
temp.exponent = 0;
int bitsCalculated = 0;
while (bitsCalculated < bits)
{
int i;
for (i = 0; (temp.exponent == 0); i++)
{
temp.mantissa.SquareHiFast(scratch);
int shift = temp.mantissa.Normalise();
temp.exponent += 1 - shift;
if (i + bitsCalculated >= bits) break;
}
pow2.MulPow2(-i);
result.Add(pow2);
temp.exponent = 0;
bitsCalculated += i;
}
this.Assign(result);
}
private static BigFloat R(BigFloat a0, BigFloat b0)
{
//Precision extend taken out.
int bits = a0.mantissa.Precision.NumBits;
PrecisionSpec extendedPres = new PrecisionSpec(bits, PrecisionSpec.BaseType.BIN);
BigFloat an = new BigFloat(a0, extendedPres);
BigFloat bn = new BigFloat(b0, extendedPres);
BigFloat sum = new BigFloat(extendedPres);
BigFloat term = new BigFloat(extendedPres);
BigFloat temp1 = new BigFloat(extendedPres);
BigFloat one = new BigFloat(1, extendedPres);
int iteration = 0;
for (iteration = 0; ; iteration++)
{
//Get the sum term for this iteration.
term.Assign(an);
term.Mul(an);
temp1.Assign(bn);
temp1.Mul(bn);
//term = an^2 - bn^2
term.Sub(temp1);
//term = 2^(n-1) * (an^2 - bn^2)
term.exponent += iteration - 1;
sum.Add(term);
if (term.exponent < -(bits - 8)) break;
//Calculate the new AGM estimates.
temp1.Assign(an);
an.Add(bn);
//a(n+1) = (an + bn) / 2
an.MulPow2(-1);
//b(n+1) = sqrt(an*bn)
bn.Mul(temp1);
bn.Sqrt();
}
one.Sub(sum);
one = one.Reciprocal();
return new BigFloat(one, a0.mantissa.Precision);
}
/// <summary>
/// Two-variable iterative square root, taken from
/// http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#A_two-variable_iterative_method
/// </summary>
public void Sqrt()
{
if (mantissa.Sign || IsSpecialValue)
{
if (SpecialValue == SpecialValueType.ZERO)
{
return;
}
if (SpecialValue == SpecialValueType.INF_MINUS || mantissa.Sign)
{
SetNaN();
}
return;
}
BigFloat temp2;
BigFloat temp3 = new BigFloat(mantissa.Precision);
BigFloat three = new BigFloat(3, mantissa.Precision);
int exponentScale = 0;
//Rescale to 0.5 <= x < 2
if (exponent < -1)
{
int diff = -exponent;
if ((diff & 1) != 0)
{
diff--;
}
exponentScale = -diff;
exponent += diff;
}
else if (exponent > 0)
{
if ((exponent & 1) != 0)
{
exponentScale = exponent + 1;
exponent = -1;
}
else
{
exponentScale = exponent;
exponent = 0;
}
}
temp2 = new BigFloat(this);
temp2.Sub(new BigFloat(1, mantissa.Precision));
//if (temp2.mantissa.IsZero())
//{
// exponent += exponentScale;
// return;
//}
int numBits = mantissa.Precision.NumBits;
while ((exponent - temp2.exponent) < numBits && temp2.SpecialValue != SpecialValueType.ZERO)
{
//a(n+1) = an - an*cn / 2
temp3.Assign(this);
temp3.Mul(temp2);
temp3.MulPow2(-1);
this.Sub(temp3);
//c(n+1) = cn^2 * (cn - 3) / 4
temp3.Assign(temp2);
temp2.Sub(three);
temp2.Mul(temp3);
temp2.Mul(temp3);
temp2.MulPow2(-2);
}
exponent += (exponentScale >> 1);
}
