fourier.h

c的快速傅立叶变换程序包

/*============================================================================

       fourier.h  -  Don Cross <[e-mail]>

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

       Contains definitions for doing Fourier transforms
       and inverse Fourier transforms.

============================================================================*/

#ifdef __cplusplus
extern "C" {
#endif

/*
**   fft() computes the Fourier transform or inverse transform
**   of the complex inputs to produce the complex outputs.
**   The number of samples must be a power of two to do the
**   recursive decomposition of the FFT algorithm.
**   See Chapter 12 of "Numerical Recipes in FORTRAN" by
**   Press, Teukolsky, Vetterling, and Flannery,
**   Cambridge University Press.
**
**   Notes:  If you pass ImaginaryIn = NULL, this function will "pretend"
**           that it is an array of all zeroes.  This is convenient for
**           transforming digital samples of real number data without
**           wasting memory.
*/

void fft_double (
    unsigned  NumSamples,          /* must be a power of 2 */
    int       InverseTransform,    /* 0=forward FFT, 1=inverse FFT */
    double   *RealIn,              /* array of input's real samples */
    double   *ImaginaryIn,         /* array of input's imag samples */
    double   *RealOut,             /* array of output's reals */
    double   *ImaginaryOut );      /* array of output's imaginaries */


void fft_float (
    unsigned  NumSamples,          /* must be a power of 2 */
    int       InverseTransform,    /* 0=forward FFT, 1=inverse FFT */
    float    *RealIn,              /* array of input's real samples */
    float    *ImaginaryIn,         /* array of input's imag samples */
    float    *RealOut,             /* array of output's reals */
    float    *ImaginaryOut );      /* array of output's imaginaries */


int IsPowerOfTwo ( unsigned x );
unsigned NumberOfBitsNeeded ( unsigned PowerOfTwo );
unsigned ReverseBits ( unsigned index, unsigned NumBits );

/*
**   The following function returns an "abstract frequency" of a
**   given index into a buffer with a given number of frequency samples.
**   Multiply return value by sampling rate to get frequency expressed in Hz.
*/
double Index_to_frequency ( unsigned NumSamples, unsigned Index );

#ifdef __cplusplus
}
#endif


/*--- end of file fourier.h ---*/