fft.h

用于进行一维和二维的傅利叶变换及其逆变换

/**********************************************************************

  FFT.h

  Dominic Mazzoni

  September 2000

  This file contains a few FFT routines, including a real-FFT
  routine that is almost twice as fast as a normal complex FFT,
  and a power spectrum routine which is more convenient when
  you know you don't care about phase information.

  Some of this code was based on a free implementation of an FFT
  by Don Cross, available on the web at:

    http://www.intersrv.com/~dcross/fft.html

  The basic algorithm for his code was based on Numerican Recipes
  in Fortran.  I optimized his code further by reducing array
  accesses, caching the bit reversal table, and eliminating
  float-to-double conversions, and I added the routines to
  calculate a real FFT and a real power spectrum.

  Note: all of these routines use single-precision floats.
  I have found that in practice, floats work well until you
  get above 8192 samples.  If you need to do a larger FFT,
  you need to use doubles.

**********************************************************************/

/*
 * This is the function you will use the most often.
 * Given an array of floats, this will compute the power
 * spectrum by doing a Real FFT and then computing the
 * sum of the squares of the real and imaginary parts.
 * Note that the output array is half the length of the
 * input array, and that NumSamples must be a power of two.
 */

void PowerSpectrum(int       NumSamples,
				  float    *In,
				  float    *Out );

/*
 * Computes an FFT when the input data is real but you still
 * want complex data as output.  The output arrays are half
 * the length of the input, and NumSamples must be a power of
 * two.
 */

void RealFFT(int       NumSamples,
			 float    *RealIn,
			 float    *RealOut,
			 float    *ImagOut );

/*
 * Computes a FFT of complex input and returns complex output.
 * Currently this is the only function here that supports the
 * inverse transform as well.
 */

void FFT (int       NumSamples,
		  bool      InverseTransform,
		  float    *RealIn,
		  float    *ImagIn,
		  float    *RealOut,
		  float    *ImagOut );