说明：  傅立叶变换与傅立叶逆变换，使用的是整型数据。一次变换时间15MS左右，正反变换30MS左右。已经在STM32F1系列（因为没有浮点运算，只能整型运算。）的上运行测试OK。
( Fourier transform and inverse Fourier transform, using integer data. A transition time around 15MS, transform pros around 30MS. Has STM32F1 series (because there is no floating point, integer arithmetic only.) The test run OK.)