public static NormalisedDecimal Create(BigInteger frac, int binaryExponent)
{
// estimate pow2&pow10 first, perform optional mulShift, then normalize
int pow10;
if (binaryExponent > 49 || binaryExponent < 46)
{
// working with ints (left Shifted 20) instead of doubles
// x = 14.5 - binaryExponent * log10(2);
int x = (29 << 19) - binaryExponent * LOG_BASE_10_OF_2_TIMES_2_POW_20;
x += C_2_POW_19; // round
pow10 = -(x >> 20);
}
else
{
pow10 = 0;
}
MutableFPNumber cc = new MutableFPNumber(frac, binaryExponent);
if (pow10 != 0)
{
cc.multiplyByPowerOfTen(-pow10);
}
switch (cc.Get64BitNormalisedExponent())
{
case 46:
if (cc.IsAboveMinRep())
{
break;
}
goto case 44;
case 44:
case 45:
cc.multiplyByPowerOfTen(1);
pow10--;
break;
case 47:
case 48:
break;
case 49:
if (cc.IsBelowMaxRep())
{
break;
}
goto case 50;
case 50:
cc.multiplyByPowerOfTen(-1);
pow10++;
break;
default:
throw new InvalidOperationException("Bad binary exp " + cc.Get64BitNormalisedExponent() + ".");
}
cc.Normalise64bit();
return cc.CreateNormalisedDecimal(pow10);
}
/**
* Convert to an equivalent {@link ExpandedDouble} representation (binary frac and exponent).
* The resulting transformed object is easily Converted to a 64 bit IEEE double:
* <ul>
* <li>bits 2-53 of the {@link #GetSignificand()} become the 52 bit 'fraction'.</li>
* <li>{@link #GetBinaryExponent()} is biased by 1023 to give the 'exponent'.</li>
* </ul>
* The sign bit must be obtained from somewhere else.
* @return a new {@link NormalisedDecimal} normalised to base 2 representation.
*/
public ExpandedDouble NormaliseBaseTwo()
{
MutableFPNumber cc = new MutableFPNumber(ComposeFrac(), 39);
cc.multiplyByPowerOfTen(_relativeDecimalExponent);
cc.Normalise64bit();
return cc.CreateExpandedDouble();
}