/// <summary>e次幂</summary>
public static BigNumber Exp(BigNumber value, int precision)
{
BigNumber sum = new BigNumber("0");
for (BigNumber n = new BigNumber("0"); ; n++)
{
BigNumber r = BigNumber.Division(value.Power(n), n.Factorial(), precision + 1);
if (r.GetPrecision(0) > precision)
{
break;
}
sum = sum + r;
}
Remove(sum, precision);
return(sum);
}
/// <summary>计算value^pow</summary>
static internal BigNumber Power(BigNumber value, BigNumber pow, int precision)
{
if (pow.DecimalPart.Count != 0 && !value.IsPlus) //第一个条件是小数次幂，第二个条件是负数
{
throw new ExpressionException("只有正数才有小数次幂");
}
BigNumber result = new BigNumber("1");
for (BigNumber i = new BigNumber("1"); i.CompareTo(pow) != 1; i++)
{
result = result * value;
}
BigNumber two = new BigNumber("2");
int n = 1;
BigNumber tt = new BigNumber(new List <int>(), pow.DecimalPart, true) * two;
while (true)
{
// 如果整数部分为1，那么就得进行一次2^n开方运算
if (tt.IntPart.Count == 1 && tt.IntPart[0] == 1)
{
tt.IntPart.Clear();
BigNumber r = Root(value, n, precision + 1);
if (r.GetPrecision(1) >= precision / BigNumber.OneCount + 2)
{
break;
}
result = result * r;
}
else if (tt.IsZero())
{
break;
}
tt = tt * two;
n++;
}
result.KeepPrecision(precision);
return(result);
}