fft library for mbed

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## FFT.cpp

Committer:
Suky
Date:
2011-02-11
Revision:
0:e3af07c00c13

### File content as of revision 0:e3af07c00c13:

/*
@file FFT.cpp
@version: 1.0
@author: Suky
@web www.micros-designs.com.ar
@date 10/02/11
*/
#include "FFT.h"

// Extracted from Numerical Recipes in C
void vFFT(float data[], unsigned int nn){
/*Replaces data[1..2*nn] by its discrete Fourier transform, if isign is input as 1; or replaces
data[1..2*nn] by nn times its inverse discrete Fourier transform, if isign is input as -1.
data is a complex array of length nn or, equivalently, a real array of length 2*nn. nn MUST
be an integer power of 2 (this is not checked for!).*/
unsigned int n,mmax,m,j,istep,i;
double wtemp,wr,wpr,wpi,wi,theta;
float tempr,tempi;

#define SWAP(a,b) tempr=(a);(a)=(b);(b)=tempr

n=nn << 1;
j=1;
for (i=1;i<n;i+=2) {
if(j>i){
SWAP(data[j],data[i]);
SWAP(data[j+1],data[i+1]);
}
m=n >> 1;
while (m >= 2 &&j>m){
j-=m;
m >>= 1;
}
j+=m;
}

mmax=2;
while (n > mmax) {
istep=mmax << 1;
theta=(6.28318530717959/mmax);
wtemp=sin(0.5*theta);
wpr = -2.0*wtemp*wtemp;
wpi=sin(theta);
wr=1.0;
wi=0.0;
for (m=1;m<mmax;m+=2) {
for (i=m;i<=n;i+=istep) {
j=i+mmax;
tempr=wr*data[j]-wi*data[j+1];
tempi=wr*data[j+1]+wi*data[j];
data[j]=data[i]-tempr;
data[j+1]=data[i+1]-tempi;
data[i] += tempr;
data[i+1] += tempi;
}
wr=(wtemp=wr)*wpr-wi*wpi+wr;
wi=wi*wpr+wtemp*wpi+wi;
}
mmax=istep;
}
}

// Extracted from Numerical Recipes in C
void vRealFFT(float data[], unsigned int n){
/*Calculates the Fourier transform of a set of n real-valued data points. Replaces this data (which
is stored in array data[1..n]) by the positive frequency half of its complex Fourier transform.
The real-valued rst and last components of the complex transform are returned as elements
data[1] and data[2], respectively. n must be a power of 2. This routine also calculates the
inverse transform of a complex data array if it is the transform of real data. (Result in this case
must be multiplied by 2/n.)*/
unsigned long i,i1,i2,i3,i4,np3;
float c1=0.5,c2,h1r,h1i,h2r,h2i;
double wr,wi,wpr,wpi,wtemp,theta;
theta=3.141592653589793/(double) (n>>1);

c2 = -0.5;
vFFT(data,n>>1);
wtemp=sin(0.5*theta);
wpr = -2.0*wtemp*wtemp;
wpi=sin(theta);
wr=1.0+wpr;
wi=wpi;
np3=n+3;
for (i=2;i<=(n>>2);i++) {
i4=1+(i3=np3-(i2=1+(i1=i+i-1)));
h1r=c1*(data[i1]+data[i3]);
h1i=c1*(data[i2]-data[i4]);
h2r = -c2*(data[i2]+data[i4]);
h2i=c2*(data[i1]-data[i3]);
data[i1]=h1r+wr*h2r-wi*h2i;
data[i2]=h1i+wr*h2i+wi*h2r;
data[i3]=h1r-wr*h2r+wi*h2i;
data[i4] = -h1i+wr*h2i+wi*h2r;
wr=(wtemp=wr)*wpr-wi*wpi+wr;
wi=wi*wpr+wtemp*wpi+wi;
}
data[1] = (h1r=data[1])+data[2];
data[2] = h1r-data[2];

}

void vCalPowerf(float Input[],float Power[], unsigned int n){
unsigned char k,j;

for(k=0,j=0;k<n;k++,j+=2){
Power[k]=sqrt(Input[j]*Input[j]+Input[j+1]*Input[j+1]);
}
}

void vCalPowerInt(float Input[],unsigned char Power[], unsigned int n){
unsigned char k,j;

for(k=0,j=0;k<n;k++,j+=2){
Power[k]=sqrt(Input[j]*Input[j]+Input[j+1]*Input[j+1]);
}
}

void vCalPowerLog(float Input[],unsigned char Power[], unsigned int n){
unsigned char k,j;
float Temp;

for(k=0,j=0;k<n;k++,j+=2){
if((Input[j]!=0) && (Input[j+1]!=0)){
Temp=sqrt(Input[j]*Input[j]+Input[j+1]*Input[j+1]);
Power[k]=10.0*log10(Temp);
}else{
Power[k]=0;
}
}

}