kiss_fft.h

#ifndef KISS_FFT_H
#define KISS_FFT_H

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <string.h>

#define KISS_FFT_MALLOC malloc
#define KISS_FFT_FREE free

typedef struct {
    double r;
    double i;
} kiss_fft_cpx;

typedef struct kiss_fft_state* kiss_fft_cfg;

#include "_kiss_fft_guts.h"

/* 
 *  kiss_fft_alloc
 *  
 *  Initialize a FFT (or IFFT) algorithm's cfg/state buffer.
 *
 *  typical usage:      kiss_fft_cfg mycfg=kiss_fft_alloc(1024,0); for FFT
 *                      kiss_fft_cfg mycfg=kiss_fft_alloc(1024,1); for IFFT
 *
 *  The return value from fft_alloc is a cfg buffer used internally
 *  by the fft routine or NULL.
 *
 *  The inverse FFT is calculated if inverse_fft is non-zero.
 *
 *  If lenmem is NULL, then kiss_fft_alloc will allocate a cfg buffer using malloc.
 *  The returned value should be free()d when done to avoid memory leaks.
 *  
 *  The state can be placed in a user supplied buffer 'mem':
 *  If lenmem is not NULL and mem is not NULL and *lenmem is large enough,
 *      then the function places the cfg in mem and the size used in *lenmem
 *      and returns mem.
 *  
 *  If lenmem is not NULL and ( mem is NULL or *lenmem is not large enough),
 *      then the function returns NULL and places the minimum cfg 
 *      buffer size in *lenmem.
 * */

kiss_fft_cfg kiss_fft_alloc(int nfft,int inverse_fft,void * mem = nullptr,size_t * lenmem = nullptr); 

/*
 * kiss_fft(cfg,in_out_buf)
 *
 * Perform an FFT on a complex input buffer.
 * for a forward FFT,
 * fin should be  f[0] , f[1] , ... ,f[nfft-1]
 * fout will be   F[0] , F[1] , ... ,F[nfft-1]
 * Note that each element is complex and can be accessed like
    f[k].r and f[k].i
 * */
void kiss_fft(kiss_fft_cfg cfg,const kiss_fft_cpx *fin,kiss_fft_cpx *fout);

/*
 A more generic version of the above function. It reads its input from every Nth sample.
 * */
void kiss_fft_stride(kiss_fft_cfg cfg,const kiss_fft_cpx *fin,kiss_fft_cpx *fout,int fin_stride);

/* If kiss_fft_alloc allocated a buffer, it is one contiguous 
   buffer and can be simply free()d when no longer needed*/
#define kiss_fft_free free

/*
 * Returns the smallest integer k, such that k>=n and k has only "fast" factors (2,3,5)
 */
int kiss_fft_next_fast_size(int n);

/* for real ffts, we need an even size */
#define kiss_fftr_next_fast_size_real(n) \
        (kiss_fft_next_fast_size( ((n)+1)>>1)<<1)

#endif