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fft.cpp
145 lines (112 loc) · 3.38 KB
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fft.cpp
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/*
* fft.cpp
* AiffPlayer
*
* Created by koji on 11/02/05.
* Copyright 2011 __MyCompanyName__. All rights reserved.
*
*/
#include "fft.h"
#include <iostream>
static const double PI = M_PI;//3.1415926536;
typedef double (*window_func)(double);
static double hamming_window(double x){
return 0.54 - 0.46*cos(2*PI*x);
}
static double hann_window(double x){
return 0.5 - 0.5*cos(2*PI*x);
}
static double blackman_window(double x){
return 0.42 -0.5*cos(2*PI*x) + 0.08*cos(4*PI*x);
}
static double zero_window(double x){
return 0;
}
static void slowFFTRecursion(
complex<double> *samples,
int length,
int start,
int skip,
complex<double>*result){
if (length == 1){
*result = samples[start];
return;
}
//compute half size
slowFFTRecursion( samples, length/2, start, skip*2, result);
slowFFTRecursion( samples, length/2, start + skip, skip*2, result + length/2);
//compute sums and differences of pairs
for (int j = 0 ; j < length/2; j++){
complex<double> t = result[j+length/2] * polar(1.0, -2*PI*j/length);
result[j + length / 2] = result[j] - t;
result[j] += t;
}
}
void slowForwardFFT(complex<double> *samples, int length, complex<double> *result){
slowFFTRecursion(samples, length, 0, 1, result);
}
static void windowing(complex<double> *samples, int length, window_func func){
for (int i = 0 ; i < length ; i++){
samples[i] *= func((double)i/(length-1));
}
}
static void rearrange(complex<double> *samples, int length){
//printf("size of int = %lu\n", sizeof(int));
//windowing
windowing(samples, length, hann_window);
static unsigned int rearrangeSize = 0; //size of rearrange table
static unsigned int *rearrange = 0;
if (rearrangeSize != length){
if(rearrange) delete [] rearrange;
rearrange = new unsigned int[length];
rearrange[0] = 0;
for (unsigned int limit = 1, bit=length/2; limit < length; limit <<=1, bit >>= 1){
for (int i = 0; i < limit; i++){
rearrange[i + limit] = rearrange[i] + bit;
}
}
for (int i = 0; i < length; i++) {
if (rearrange[i] == i) rearrange[i] = 0;
else rearrange[ rearrange[i] ] = 0;
}
rearrangeSize = length;
}
//use the rearrange table to swap elements
complex<double> t;
for (int i = 0 ; i < length; i++){
if (rearrange[i]){
t = samples[i];
samples[i] = samples[ rearrange[i] ];
samples[ rearrange[i] ] = t;
}
}
}
void fastForwardFFT(complex<double> *samples_org, int length, complex<double> *result){
for (int i = 0 ; i < length ; i++){
result[i] = samples_org[i];
//result[i] *= std::polar(1.0, -2.3);// * 3.2;
}
rearrange(result, length);
for (int halfSize = 1; halfSize < length; halfSize *= 2){
complex<double> phaseShiftStep = std::polar(1.0, -PI/halfSize);
complex<double> currentPhaseShift(1,0);
for (int fftStep = 0; fftStep < halfSize; fftStep++){
for (int i= fftStep ; i < length; i += 2*halfSize){
complex<double> t = currentPhaseShift * result[ i + halfSize];
result[i + halfSize] = result[i] - t;
result[i] += t;
}
currentPhaseShift *= phaseShiftStep;
}
//std::cout << currentPhaseShift << "\n";
}
}
void DFT(complex<double> *samples, int length, complex<double> *result){
for (int f = 0; f < length; f++){
result[f] = complex<double>(0.0);
for (int t = 0 ; t < length; t++){
complex<double> val = samples[t];
result[f] += val * polar(1.0, -2*PI*f*t/length);
}
}
}