/// <summary>
/// 求长度指令，b代表变量寄存器索引，a代表结果目标索引
/// </summary>
/// <param name="i"></param>
public void Len(Instruction i)
{
int a = 0, b = 0, c = 0;
i.ABC(ref a, ref b, ref c);
luaState.Len(b + 1);
luaState.Replace(a + 1);
}
