blocks|key|685292|text|你可以开始将this+java+snippet转换成C，作者说他已经根据你在网上找到的numerical+recipies这本书把它从C转换成了C！here|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|685293|entityMap|0|LINK|mutability|MUTABLE|url|http://blog.datasingularity.com/?p=53|1|https://rads.stackoverflow.com/amzn/click/com/0521431085|2|http://apps.nrbook.com/c/index.html^0|6|H|0|17|I|1|22|4|2|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]|$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|-4|5|6|7|Z|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]|N|$5|G|H|I|C|$J|O]]]]

You could start converting <a href="http://blog.datasingularity.com/?p=53" rel="noreferrer">this java snippet</a> to C the author states he has converted it from C based on the book <a href="https://rads.stackoverflow.com/amzn/click/com/0521431085" rel="noreferrer" rel="nofollow noreferrer">numerical recipies</a> which you find online! <a href="http://apps.nrbook.com/c/index.html" rel="noreferrer">here</a>

blocks|key|685331|text|你最好的选择是KissFFT+--顾名思义，它是simple，但它仍然相当快，而且比FFTW轻量级得多。它也是免费的，如果你想把它包含在商业产品中，FFTW需要支付高额的许可费。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|685332|entityMap|0|LINK|mutability|MUTABLE|url|http://sourceforge.net/projects/kissfft/|1|http://en.wikipedia.org/wiki/KISS_principle^0|7|7|0|O|6|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

Your best bet is <a href="http://sourceforge.net/projects/kissfft/">KissFFT</a> - as its name implies it's <a href="http://en.wikipedia.org/wiki/KISS_principle">simple</a>, 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.

blocks|key|685370|text|Here+is+a+permissively-licensed+C+library+with+a+variety+of+different+FFT+implementations，每个文件都在它自己的独立的C文件中。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|685371|entityMap|0|LINK|mutability|MUTABLE|url|http://www.kurims.kyoto-u.ac.jp/~ooura/fft.html^0|0|2H|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

<a href="http://www.kurims.kyoto-u.ac.jp/~ooura/fft.html" rel="noreferrer">Here is a permissively-licensed C library with a variety of different FFT implementations</a>, each of which is in its own self-contained C-file.

blocks|key|685403|text|此文件工作正常:只需将其复制并粘贴到您的计算机中即可。在网上冲浪时，我在维基百科的here页面上找到了这个简单的实现。页面是意大利语的，所以我用一些翻译重写了代码。Here有几乎相同的信息，但用英语写的。享受吧！|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|685404|#include+<iostream>
#include+<complex>
#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+>>=+1;
++++i%2B%2B;
++}
++return+i+-+1;
}

int+check(int+n)++++//checking+if+the+number+of+element+is+a+power+of+2
{
++return+n+>+0+&&+(n+&+(n+-+1))+==+0;
}

int+reverse(int+N,+int+n)++++//calculating+revers+number
{
++int+j,+p+=+0;
++for(j+=+1;+j+<=+log2(N);+j%2B%2B)+{
++++if(n+&+(1+<<+(log2(N)+-+j)))
++++++p+%7C=+1+<<+(j+-+1);
++}
++return+p;
}

void+ordina(complex<double>*+f1,+int+N)+//using+the+reverse+order+in+the+array
{
++complex<double>+f2[MAX];
++for(int+i+=+0;+i+<+N;+i%2B%2B)
++++f2[i]+=+f1[reverse(N,+i)];
++for(int+j+=+0;+j+<+N;+j%2B%2B)
++++f1[j]+=+f2[j];
}

void+transform(complex<double>*+f,+int+N)+//
{
++ordina(f,+N);++++//first:+reverse+order
++complex<double>+*W;
++W+=+(complex<double>+*)malloc(N+/+2+*+sizeof(complex<double>));
++W[1]+=+polar(1.,+-2.+*+M_PI+/+N);
++W[0]+=+1;
++for(int+i+=+2;+i+<+N+/+2;+i%2B%2B)
++++W[i]+=+pow(W[1],+i);
++int+n+=+1;
++int+a+=+N+/+2;
++for(int+j+=+0;+j+<+log2(N);+j%2B%2B)+{
++++for(int+i+=+0;+i+<+N;+i%2B%2B)+{
++++++if(!(i+&+n))+{
++++++++complex<double>+temp+=+f[i];
++++++++complex<double>+Temp+=+W[(i+*+a)+%25+(n+*+a)]+*+f[i+%2B+n];
++++++++f[i]+=+temp+%2B+Temp;
++++++++f[i+%2B+n]+=+temp+-+Temp;
++++++}
++++}
++++n+*=+2;
++++a+=+a+/+2;
++}
++free(W);
}

void+FFT(complex<double>*+f,+int+N,+double+d)
{
++transform(f,+N);
++for(int+i+=+0;+i+<+N;+i%2B%2B)
++++f[i]+*=+d;+//multiplying+by+step
}

int+main()
{
++int+n;
++do+{
++++cout+<<+"specify+array+dimension+(MUST+be+power+of+2)"+<<+endl;
++++cin+>>+n;
++}+while(!check(n));
++double+d;
++cout+<<+"specify+sampling+step"+<<+endl;+//just+write+1+in+order+to+have+the+same+results+of+matlab+fft(.)
++cin+>>+d;
++complex<double>+vec[MAX];
++cout+<<+"specify+the+array"+<<+endl;
++for(int+i+=+0;+i+<+n;+i%2B%2B)+{
++++cout+<<+"specify+element+number:+"+<<+i+<<+endl;
++++cin+>>+vec[i];
++}
++FFT(vec,+n,+d);
++cout+<<+"...printing+the+FFT+of+the+array+specified"+<<+endl;
++for(int+j+=+0;+j+<+n;+j%2B%2B)
++++cout+<<+vec[j]+<<+endl;
++return+0;
}|code-block|syntax|javascript|685405|entityMap|0|LINK|mutability|MUTABLE|url|https://it.wikipedia.org/wiki/Trasformata_di_Fourier_veloce|1|https://en.wikipedia.org/wiki/Fast_Fourier_transform^0|15|4|0|2A|4|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

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 <a href="https://it.wikipedia.org/wiki/Trasformata_di_Fourier_veloce" rel="noreferrer">here</a>. The page is in italian, so I re-wrote the code with some translations. <a href="https://en.wikipedia.org/wiki/Fast_Fourier_transform" rel="noreferrer">Here</a> there are almost the same informations but in english. ENJOY!

<pre><code>#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;
}
</code></pre>

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?

FFT in a single C-file

我在寻找一个C语言的FFT实现。然而，我并不是在寻找一个巨大的库(比如FFTW)，而是为了一个易于使用的C文件实现。不幸的是，我还没能找到这样的东西。有人能推荐一个简单的实现吗？

问单个C文件中的FFT
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