functions.hpp

来自「此程序基于c语言实现fft快速傅里叶变换」· HPP 代码 · 共 18 行

//生成基-2比特逆序数,以后可改为多基逆序数 
//采用移位运算实现！/ & % 
unsigned long bitinv(unsigned power,unsigned k)
{
    unsigned kk;
    unsigned long sum=0;
    power=(1<<power);
    while(k)
    {
       kk=k>>1;
       power>>=1;
       if(k-(kk<<1))
          sum+=power;
       k=kk;
    }
    return sum;
}