📄 fast fourier transform in c# (cooky-turkey) - adrian's tech blog - 博客园.htm

📁 c语言写的FFT变换源码,有多个版本,经测试,还比较好用
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<H2><A class=singleposttitle id=AjaxHolder_ctl01_TitleUrl 
href="http://www.cnblogs.com/Dah/archive/2007/08/10/850904.html">Fast Fourier 
Transform in C# (Cooky-Turkey)</A> </H2></DIV>
<DIV class=postbody>C# code snippet below is an illustration of the Cooky-Turkey 
algorithm, the performance may suck when processing huge datasets, but you can 
use arrays of double instead of arrays of complex number structure to reduce the 
performance impact by object initializations and method invocations(overloaded 
operators).<BR>Furthermore, you can use "Butterfly" computation(<A 
href="http://www.cmlab.csie.ntu.edu.tw/cml/dsp/training/coding/transform/fft.html">http://www.cmlab.csie.ntu.edu.tw/cml/dsp/training/coding/transform/fft.html</A>) 
to gain a much better performance.<BR><BR>
<DIV 
style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--><SPAN 
style="COLOR: #0000ff">private</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Complex[]&nbsp;FFT(Complex[]&nbsp;input,</SPAN><SPAN 
style="COLOR: #0000ff">bool</SPAN><SPAN 
style="COLOR: #000000">&nbsp;invert)<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">if</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(input.Length&nbsp;</SPAN><SPAN 
style="COLOR: #000000">==</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">1</SPAN><SPAN 
style="COLOR: #000000">)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">return</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Complex[]&nbsp;{&nbsp;input[</SPAN><SPAN 
style="COLOR: #000000">0</SPAN><SPAN 
style="COLOR: #000000">]&nbsp;};<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;length&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;input.Length;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;half&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;length&nbsp;</SPAN><SPAN 
style="COLOR: #000000">/</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">2</SPAN><SPAN 
style="COLOR: #000000">;<BR>&nbsp;&nbsp;&nbsp;&nbsp;Complex[]&nbsp;result&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Complex[length];<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">double</SPAN><SPAN 
style="COLOR: #000000">&nbsp;fac&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">-</SPAN><SPAN style="COLOR: #000000">2.0</SPAN><SPAN 
style="COLOR: #000000">&nbsp;</SPAN><SPAN style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Math.PI&nbsp;</SPAN><SPAN 
style="COLOR: #000000">/</SPAN><SPAN 
style="COLOR: #000000">&nbsp;length;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">if</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(invert)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fac&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">-</SPAN><SPAN 
style="COLOR: #000000">fac;<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;Complex[]&nbsp;evens&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">new</SPAN><SPAN 
style="COLOR: #000000">&nbsp;Complex[half];<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">for</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;i&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">0</SPAN><SPAN 
style="COLOR: #000000">;&nbsp;i&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;half;&nbsp;i</SPAN><SPAN 
style="COLOR: #000000">++</SPAN><SPAN 
style="COLOR: #000000">)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;evens[i]&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;input[</SPAN><SPAN 
style="COLOR: #000000">2</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;i];<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;Complex[]&nbsp;evenResult&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;FFT(evens,invert);<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;Complex[]&nbsp;odds&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;evens;<BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">for</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;i&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">0</SPAN><SPAN 
style="COLOR: #000000">;&nbsp;i&nbsp;</SPAN><SPAN 
style="COLOR: #000000">&lt;</SPAN><SPAN 
style="COLOR: #000000">&nbsp;half;&nbsp;i</SPAN><SPAN 
style="COLOR: #000000">++</SPAN><SPAN 
style="COLOR: #000000">)<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;odds[i]&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;input[</SPAN><SPAN 
style="COLOR: #000000">2</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">*</SPAN><SPAN 
style="COLOR: #000000">&nbsp;i&nbsp;</SPAN><SPAN 
style="COLOR: #000000">+</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN 
style="COLOR: #000000">1</SPAN><SPAN 
style="COLOR: #000000">];<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR>&nbsp;&nbsp;&nbsp;&nbsp;Complex[]&nbsp;oddResult&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN 
style="COLOR: #000000">&nbsp;FFT(odds,invert);<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;</SPAN><SPAN 
style="COLOR: #0000ff">for</SPAN><SPAN 
style="COLOR: #000000">&nbsp;(</SPAN><SPAN 
style="COLOR: #0000ff">int</SPAN><SPAN 
style="COLOR: #000000">&nbsp;k&nbsp;</SPAN><SPAN 
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000">&nbsp;</SPAN><SPAN
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