private static int RoundDigit(int sign, uint lastDigit, uint secondLastDigit, BigDecimal.RoundingModes roundingMode)
{
int result = -1;
switch (roundingMode)
{
case BigDecimal.RoundingModes.Up:
if (lastDigit != 0)
{
result = 1;
}
break;
case BigDecimal.RoundingModes.HalfUp:
if (lastDigit >= 5)
{
result = 1;
}
break;
case BigDecimal.RoundingModes.HalfDown:
if (lastDigit > 5)
{
result = 1;
}
break;
case BigDecimal.RoundingModes.HalfEven:
if (lastDigit > 5)
{
result = 1;
}
else if ((lastDigit == 5) && (secondLastDigit % 2 != 0))
{
result = 1;
}
break;
case BigDecimal.RoundingModes.Ceiling:
if (sign == 1 && lastDigit != 0)
{
result = 1;
}
break;
case BigDecimal.RoundingModes.Floor:
if (sign == -1 && lastDigit != 0)
{
result = 1;
}
break;
}
return(result);
}
/// <summary>
/// Limits the precision of the given Fraction.
/// </summary>
/// <param name="sign">The sign of the BigDecimal</param>
/// <param name="fraction">The fraction to limit</param>
/// <param name="digits">The number of digits to which we are limiting</param>
/// <param name="mode">The rounding mode to use when limiting</param>
/// <returns>A new fraction that has no more than <paramref name="digits"/> digits.</returns>
/// <example>
/// Consider a fraction of 123456789 using default HalfUp rounding.
/// Limit : Result
/// 1 1
/// 2 12
/// 3 123
/// 4 1234
/// 5 12346
/// 6 123457
/// 7 1234568
/// 8 12345679
/// 9 123456789
/// 10 123456789
/// </example>
public static Fraction /*!*/ LimitPrecision(int sign, Fraction /*!*/ fraction, int digits, BigDecimal.RoundingModes mode, out int offset)
{
Fraction result;
if (digits <= 0)
{
uint digit = (uint)(fraction.IsZero ? 0 : 1);
if (RoundDigit(sign, digit, 0, mode) > 0)
{
offset = 1 - digits;
return(One);
}
else
{
offset = 0;
return(Zero);
}
}
if (digits >= fraction.DigitCount)
{
offset = 0;
return(fraction);
}
// Calculate offsets of relevant digits
int secondLastDigitIndex; // i.e. fraction[digits-1]
int secondLastWordIndex;
uint secondLastDigit;
int lastDigitIndex; // i.e. fraction[digits]
int lastWordIndex;
uint lastDigit;
#if SILVERLIGHT
secondLastWordIndex = DivRem(digits - 1, BASE_FIG, out secondLastDigitIndex);
#else
secondLastWordIndex = System.Math.DivRem(digits - 1, BASE_FIG, out secondLastDigitIndex);
#endif
if (secondLastDigitIndex == BASE_FIG - 1)
{
lastWordIndex = secondLastWordIndex + 1;
lastDigitIndex = 0;
}
else
{
lastWordIndex = secondLastWordIndex;
lastDigitIndex = secondLastDigitIndex + 1;
}
// TODO: Extract these calculations out into static readonly arrays
// Mask for last digit. E.g. lastDigitIndex = 3, BASE_FIG = 9 => lastFactor = 1000000
uint lastFactor = _powers[lastDigitIndex];
// Mask for second last digit
uint secondLastFactor = _powers[secondLastDigitIndex];
// Calculate the current digits and rounding direction
secondLastDigit = (fraction._words[secondLastWordIndex] / secondLastFactor) % 10;
if (lastWordIndex < fraction.MaxPrecision)
{
lastDigit = (fraction._words[lastWordIndex] / lastFactor) % 10;
}
else
{
lastDigit = 0;
}
int round = RoundDigit(sign, lastDigit, secondLastDigit, mode);
// Create a temporary fraction used to cause the rounding in the original
result = new Fraction(lastWordIndex + 1);
Array.Copy(fraction._words, 0, result._words, 0, System.Math.Min(lastWordIndex + 1, fraction.Precision));
// Clear the digits beyond the second last digit
result._words[secondLastWordIndex] = result._words[secondLastWordIndex] - (fraction._words[secondLastWordIndex] % secondLastFactor);
if (round > 0)
{
// Increment the last digit of result by 1
Fraction temp = new Fraction(secondLastWordIndex + 1);
temp._words[secondLastWordIndex] = secondLastFactor;
result = Fraction.Add(result, temp, 0, out offset);
}
else
{
offset = 0;
}
result.Precision = System.Math.Min(secondLastWordIndex + 1, result.MaxPrecision);
return(result);
}