通过查表法来实现fft中的sin和cos，大大加快了程序的速度-Watch by the law to implement fft of sin and cos, and has been greatly speeded the speed

用差表法实现sin和cos函数，浮点运算实现采样点数可变化的fft函数-Realization of sin and cos functions, floating point differential table method of sampling points can be varied to achieve fft function