# FFT算法C语言实现

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• 2022-06-08 12:19
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FFT算法，国外网站上的，从他的例程里提取出来，相当好用！ (FFT algorithm) C语言实现版本
26334727fourier.zip
• Fourier.h
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• Fourier.cpp
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/********************************************************/ /* WARNING: */ /* This code cannot be used in any aplication */ /* without permition of the author */ /* for more information please read the license in the */ /* Numerical Recipies in C book or go to www.nr.com */ /* this is mearly an example of how to use it */ /********************************************************/ #include "StdAfx.h" #include <math.h> #include ".\fourier.h" #define SWAP(a,b) tempr=(a);(a)=(b);(b)=tempr CFourier::CFourier(void) { pi=4*atan((double)1);vector=NULL; } CFourier::~CFourier(void) {if(vector!=NULL) delete [] vector; } // FFT 1D void CFourier::ComplexFFT(float data[], unsigned long number_of_samples, unsigned int sample_rate, int sign) { //variables for the fft unsigned long n,mmax,m,j,istep,i; double wtemp,wr,wpr,wpi,wi,theta,tempr,tempi; //the complex array is real+complex so the array //as a size n = 2* number of complex samples //real part is the data[index] and //the complex part is the data[index+1] //new complex array of size n=2*sample_rate if(vector!=NULL) delete [] vector; vector=new float [2*sample_rate]; //put the real array in a complex array //the complex part is filled with 0's //the remaining vector with no data is filled with 0's for(n=0; n<sample_rate;n++) { if(n<number_of_samples) vector[2*n]=data[n]; else vector[2*n]=0; vector[2*n+1]=0; } //binary inversion (note that the indexes //start from 0 witch means that the //real part of the complex is on the even-indexes //and the complex part is on the odd-indexes) n=sample_rate << 1; j=0; for (i=0;i<n/2;i+=2) { if (j > i) { SWAP(vector[j],vector[i]); SWAP(vector[j+1],vector[i+1]); if((j/2)<(n/4)){ SWAP(vector[(n-(i+2))],vector[(n-(j+2))]); SWAP(vector[(n-(i+2))+1],vector[(n-(j+2))+1]); } } m=n >> 1; while (m >= 2 && j >= m) { j -= m; m >>= 1; } j += m; } //end of the bit-reversed order algorithm //Danielson-Lanzcos routine mmax=2; while (n > mmax) { istep=mmax << 1; theta=sign*(2*pi/mmax); wtemp=sin(0.5*theta); wpr = -2.0*wtemp*wtemp; wpi=sin(theta); wr=1.0; wi=0.0; for (m=1;m<mmax;m+=2) { for (i=m;i<=n;i+=istep) { j=i+mmax; tempr=wr*vector[j-1]-wi*vector[j]; tempi=wr*vector[j]+wi*vector[j-1]; vector[j-1]=vector[i-1]-tempr; vector[j]=vector[i]-tempi; vector[i-1] += tempr; vector[i] += tempi; } wr=(wtemp=wr)*wpr-wi*wpi+wr; wi=wi*wpr+wtemp*wpi+wi; } mmax=istep; } //end of the algorithm //determine the fundamental frequency //look for the maximum absolute value in the complex array fundamental_frequency=0; for(i=2; i<=sample_rate; i+=2) { if((pow(vector[i],2)+pow(vector[i+1],2))>(pow(vector[fundamental_frequency],2)+pow(vector[fundamental_frequency+1],2))){ fundamental_frequency=i; } } //since the array of complex has the format [real][complex]=>[absolute value] //the maximum absolute value must be ajusted to half fundamental_frequency=(long)floor((float)fundamental_frequency/2); }

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