C# 计算传入的时间距离今天的时间差

/// <summary>
/// 计算传入的时间距离今天的时间差
/// </summary>
/// <param name="dt"></param>
/// <param name="yy"></param>
/// <param name="mm"></param>
/// <param name="dd"></param>
public void getcriminalyx(datetime dt, out int yy, out int mm, out int dd)
{
datetime now = datetime.now;
yy = mm = dd = 0;
if (dt.year > 9000 || dt.year == 1900)
{
return;
}
if (dt <= now)
{
return;
}
stringbuilder str = new stringbuilder();
int dt_y = dt.year;
int dt_m = dt.month;
int dt_d = dt.day;
int now_y = datetime.now.year;
int now_m = datetime.now.month;
int now_d = datetime.now.day;
yy = dt_y - now_y;
mm = dt_m - now_m;
dd = 0;

int dt_m_sy = 0;
if (dt_d < now_d)
{
mm -= 1;
dt_m_sy = dt_m - 1;
if (dt_m_sy == 0)
{
dt_m_sy = 12;
}
if (dt_m_sy == 2)
{
dt_m_sy = dt_y % 4 == 0 ? 29 : 28;
}
else
{
dt_m_sy = dt_m_sy == 2 || dt_m_sy == 4 || dt_m_sy == 6 || dt_m_sy == 9 || dt_m_sy == 11 ? 30 : 31;
}
dt_d += dt_m_sy;
}
dd = dt_d - now_d;
if (mm < 0)
{
yy -= 1;
mm += 12;
}
}