/
fft3.c
executable file
·82 lines (69 loc) · 1.51 KB
/
fft3.c
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#include "fft.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <limits.h>
static complex_t twiddle(int N, int k){
complex_t rs;
rs.re = cos((2*M_PI*k)/N);
rs.im = -sin((2*M_PI*k)/N);
return rs;
}
static int bit_len(int n){
int i =0;
for(i = 0;i < 32; ++i){
if( (n & (1 << i)) ){
break;
}
}
return i+1;
}
static unsigned bit_swap(unsigned num, int n){
unsigned rs = 0;
int i ;
for(i = 0;i < n; ++i){
if( (num & (1<<i)) == (1<<i) ){
rs += (1<<(n-i-1));
}
}
return rs;
}
static void jig_input(complex_t* input, complex_t* output, int n){
int i = 0;
int size = bit_len(n);
--size;
for( i = 0; i < n ;++i){
output[bit_swap(i,size)] = input[i];
}
}
int _fft(complex_t* input, complex_t* output, unsigned n){
jig_input(input,output,n);
int level = 0;
int num_levels = bit_len(n);
int block_size = 2;
for( level = num_levels-1; level != 0 ; --level){
int num_blocks = n / block_size;
int segment = 0;
complex_t Y_k,Z_k,W;
complex_t* out;
for(segment = 0; segment < num_blocks; ++segment){
out = output + segment*block_size;
int i = 0;
for( i = 0; i< block_size/2; ++i){
Y_k = out[i];
Z_k = out[i +block_size/2];
W = twiddle(block_size, i);
complex_t temp;
complex_mult(&W,&Z_k,&temp);
out[i].re = Y_k.re + temp.re;
out[i].im = Y_k.im + temp.im;
out[i + block_size/2].re = Y_k.re - temp.re;
out[i + block_size/2].im = Y_k.im - temp.im;
}
}
block_size *= 2;
}
return 1;
}