private static double TryRoundDoubleQuick(double value, int decimals, MidpointRounding midpointRounding)
{
// Try a fast round based on ideas from: http://www.coderanch.com/t/582520/java/java/fast-method.
// The problem is that when we multiply by a power of ten we might - due to inherent double
// inaccuaracy - end up with a value that rounds differently to what we expect.
// Therefore we round two values just slighly larger/smaller that the value
// we try to round. If the results are equal, we're done. If they are not,
// we fail with double.NaN.
if (RoundPower10Double == null) // can't use static initializer in a framework extension class.
{
RoundPower10Double = new[] { 1E0, 1E1, 1E2, 1E3, 1E4, 1E5, 1E6, 1E7, 1E8, 1E9, 1E10, 1E11, 1E12, 1E13, 1E14, 1E15 }
}
;
var factor = RoundPower10Double[decimals];
double y = value * factor;
var threshold = Math.Ulp(y) * RoundSafetyFactor;
double d1, d2;
if (midpointRounding == MidpointRounding.AwayFromZero)
{
if (y < 0)
{
y -= 0.5;
d1 = Math.Ceiling(y + threshold);
d2 = Math.Ceiling(y - threshold);
}
else
{
y += 0.5;
d1 = Math.Floor(y + threshold);
d2 = Math.Floor(y - threshold);
}
}
else
{
d1 = Math.Rint(y + threshold);
d2 = Math.Rint(y - threshold);
}
if (d1 == d2)
{
return(d1 / factor);
}
return(double.NaN);
}
