/// <summary>
/// 减法，有效位数与加法类似，取决于绝对误差最大的数
/// </summary>
/// <param name="a"></param>
/// <param name="b"></param>
/// <returns></returns>
public static SKSpecialDecimal operator -(SKSpecialDecimal a, SKSpecialDecimal b)
{
SKSpecialDecimal b_copy = new SKSpecialDecimal(b);
b_copy.inverse();
return(a + b_copy);
}
