/// <summary>
/// Construct a BigFloat from a double-precision floating point number
/// </summary>
/// <param name="value"></param>
/// <param name="mantissaPrec"></param>
public BigFloat(double value, PrecisionSpec mantissaPrec)
{
if (value == 0.0)
{
Init(mantissaPrec);
return;
}
bool sign = (value < 0) ? true : false;
long bits = BitConverter.DoubleToInt64Bits(value);
// Note that the shift is sign-extended, hence the test against -1 not 1
int valueExponent = (int)((bits >> 52) & 0x7ffL);
long valueMantissa = bits & 0xfffffffffffffL;
//The mantissa is stored with the top bit implied.
valueMantissa = valueMantissa | 0x10000000000000L;
//The exponent is biased by 1023.
exponent = valueExponent - 1023;
//Round the number of bits to the nearest word.
int mbWords = ((mantissaPrec.NumBits) >> 5);
if ((mantissaPrec.NumBits & 31) != 0) mbWords++;
int newManBits = mbWords << 5;
mantissa = new BigInt(new PrecisionSpec(newManBits, PrecisionSpec.BaseType.BIN));
//scratch = new BigInt(new PrecisionSpec(newManBits, PrecisionSpec.BaseType.BIN));
if (newManBits >= 64)
{
//The mantissa is 53 bits now, so add 11 to put it in the right place.
mantissa.SetHighDigits(valueMantissa << 11);
}
else
{
//To get the top word of the mantissa, shift up by 11 and down by 32 = down by 21
mantissa.SetHighDigit((uint)(valueMantissa >> 21));
}
mantissa.Sign = sign;
}
