FFT in a single C-file

Question

I was looking for a FFT implementation in C  However  I am not looking for a huge library  like FFTW  but for a easy to use single C-file implementation  Unfortunately I haven t been able to find anything like this    Can someone recommend a simple implementation

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You could start converting this java snippet to C the author states he has converted it from C based on the book numerical recipies which you find online  here

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Here is a permissively-licensed C library with a variety of different FFT implementations  each of which is in its own self-contained C-file

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Your best bet is KissFFT - as its name implies it s simple  but it s still quite respectably fast  and a lot more lightweight than FFTW  It s also free  wheras FFTW requires a hefty licence fee if you want to include it in a commercial product

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This file works properly as it is  just copy and paste in your computer  Surfing on the web I have found this easy implementation on wikipedia page here  The page is in italian  so I re-wrote the code with some translations  Here there are almost the same informations but in english  ENJOY    include  lt iostream gt   include  lt complex gt   define MAX 200  using namespace std    define M PI 3 1415926535897932384  int log2 int N       function to calculate the log2    of int numbers       int k   N  i   0    while k        k  gt  gt   1      i          return i - 1     int check int n       checking if the number of element is a power of 2     return n  gt  0  amp  amp   n  amp   n - 1      0     int reverse int N  int n       calculating revers number     int j  p   0    for j   1  j  lt   log2 N   j          if n  amp   1  lt  lt   log2 N  - j          p    1  lt  lt   j - 1         return p     void ordina complex lt double gt   f1  int N    using the reverse order in the array     complex lt double gt  f2 MAX     for int i   0  i  lt  N  i        f2 i    f1 reverse N  i      for int j   0  j  lt  N  j        f1 j    f2 j      void transform complex lt double gt   f  int N         ordina f  N        first  reverse order   complex lt double gt   W    W    complex lt double gt    malloc N   2   sizeof complex lt double gt       W 1    polar 1   -2    M PI   N     W 0    1    for int i   2  i  lt  N   2  i        W i    pow W 1   i     int n   1    int a   N   2    for int j   0  j  lt  log2 N   j          for int i   0  i  lt  N  i            if   i  amp  n             complex lt double gt  temp   f i           complex lt double gt  Temp   W  i   a     n   a     f i   n           f i    temp   Temp          f i   n    temp - Temp                    n    2      a   a   2        free W      void FFT complex lt double gt   f  int N  double d      transform f  N     for int i   0  i  lt  N  i        f i     d    multiplying by step    int main       int n    do       cout  lt  lt   specify array dimension  MUST be power of 2    lt  lt  endl      cin  gt  gt  n      while  check n      double d    cout  lt  lt   specify sampling step   lt  lt  endl    just write 1 in order to have the same results of matlab fft      cin  gt  gt  d    complex lt double gt  vec MAX     cout  lt  lt   specify the array   lt  lt  endl    for int i   0  i  lt  n  i          cout  lt  lt   specify element number     lt  lt  i  lt  lt  endl      cin  gt  gt  vec i         FFT vec  n  d     cout  lt  lt      printing the FFT of the array specified   lt  lt  endl    for int j   0  j  lt  n  j        cout  lt  lt  vec j   lt  lt  endl    return 0

[c] FFT in a single C-file

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