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fft_funct.c
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fft_funct.c
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#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "fft_funct.h" // definition of fft_funct
#define PI 3.14159265358979323
#define N 4096 // maximum number of samples
// coefficients
double Wre[N/2];
double Wim[N/2];
// CalcolaW() declaration
void CalcolaW(int n);
void fft_funct(double * buffer, int size)
{
int posizioni[N] = {0};
int i,j;
int numerobit;
int appoggio=0;
int NC;
float scarto;
// variables for calculus of steps
int k=0;
int v=0;
int a,b;
int incremento;
int nBlocchi,elBlocco;
// temporary vectors for storing values between steps
double Xreapp[N] = {0};
double Ximapp[N] = {0};
// sequences
double Xre[N] = {0};
double Xim[N] = {0};
scarto = log2(size)-((int)log2(size));
if (scarto >= 0.5)
NC = pow(2,(((int)log2(size))+1));
else
NC = pow(2,((int)log2(size)));
// bit inversion
numerobit=log2(NC);
for (i=0; i<NC; i++)
{
appoggio =i;
posizioni[i] = (appoggio&0x0001)|(posizioni[i]);
for (j=0; j<(numerobit-1); j++)
{
appoggio = appoggio >> 1;
posizioni[i] = ((posizioni[i])<<1);
posizioni[i] = (appoggio&0x0001)|(posizioni[i]);
}
}
printf("size = %d \n", size);
printf("NC = %d \n", NC);
// sequences initialization
i=0;
if (size>=NC)
{
while(i<NC)
{
Xre[posizioni[i]] = buffer[i];
i=i+1;
}
}
else
{
while(i<size)
{
Xre[posizioni[i]] = buffer[i];
i=i+1;
}
while(i<NC)
{
Xre[posizioni[i]] = 0.0;
i=i+1;
}
}
// coefficients calculation
CalcolaW(NC);
for(i=0;i<NC;i++)
{
Xreapp[i] = Xre[i];
//Ximapp[i] = Xim[i];
}
for(i=0;i<numerobit;i++)
{
nBlocchi = NC /pow(2,i+1);
incremento = NC /pow(2,i+1);
elBlocco= NC/nBlocchi;
for (a=0; a<nBlocchi; a++)
{
for(b=0; b<(elBlocco/2); b++)
{
Xre[k]=Xreapp[k]+ (Wre[v]*Xreapp[k+(int)(pow(2,i))] - Wim[v]*Ximapp[k+(int)(pow(2,i))]);
Xim[k]=Ximapp[k]+ (Wim[v]*Xreapp[k+(int)(pow(2,i))] + Wre[v]*Ximapp[k+(int)(pow(2,i))]);
Xre[k+(int)(pow(2,i))]=Xreapp[k]- (Wre[v]*Xreapp[k+(int)(pow(2,i))] - Wim[v]*Ximapp[k+(int)(pow(2,i))]);
Xim[k+(int)(pow(2,i))]=Ximapp[k]- (Wim[v]*Xreapp[k+(int)(pow(2,i))] + Wre[v]*Ximapp[k+(int)(pow(2,i))]);
v = v + incremento;
if (i != 0)
k = k+1;
}
k = a*(elBlocco);
k = k + (elBlocco);
v=0;
}
k=0;
// writing of next temporary vectors
for(j=0;j<NC;j++)
{
Xreapp[j] = Xre[j];
Ximapp[j] = Xim[j];
}
}
// amplitude calculation
for(i=0;i<NC/2;i++)
{
buffer[i] = pow(((Xre[i]*Xre[i])+(Xim[i]*Xim[i])),0.5)/NC*2.0;
}
FILE* fptxtasc;
fptxtasc = fopen("ascisse.txt","w");
float step=44100/NC;
for(i=0; i<(NC/2); i++)
{
fprintf(fptxtasc,"%2.3f\n",i*step);
}
}
// CalcolaW() definition
void CalcolaW(int n)
{
int i;
for (i=0;i<(n/2);i++)
{
Wre[i]=cos(2*PI*i/n);
Wim[i]=-sin(2*PI*i/n);
}
}