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#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <complex.h>
#include <math.h>
// Needed for option parsing
#include <unistd.h>
#include <string.h>
#define MAX_FILE_SIZE 10000
typedef uint16_t index_t;
typedef complex double val_t;
// Make a better version of this
index_t reverse_bits(index_t i, unsigned fft_size)
{
unsigned n = fft_size;
index_t reverse = 0;
while (n--) {
reverse <<= 1;
reverse |= i & 1;
i >>= 1;
}
return reverse;
}
val_t twiddle(index_t N, int k)
{
val_t in = (2 * M_PI)/(double)N;
val_t res = cexp(-in * k * I);
return res;
}
void butterfly_single(val_t *buf, index_t a, index_t b, val_t twid)
{
val_t common = twid * buf[b];
buf[b] = buf[a] - common;
buf[a] += common;
}
void butterfly(val_t *buf, unsigned depth, index_t n, index_t N)
{
if (n == 2) {
butterfly_single(buf, 0, 1, twiddle(N, 0));
return;
}
n = n/2;
index_t step = pow(2, depth);
for (index_t i = 0; i < n; i++) {
butterfly_single(buf, i, i + n, twiddle(N, i * step));
}
}
void fft_inplace_recur(val_t *buf, unsigned depth, index_t n, index_t N)
{
if (n > 2) {
index_t split = n/2;
fft_inplace_recur(buf, depth+1, split, N);
fft_inplace_recur(buf+split, depth+1, split, N);
}
butterfly(buf, depth, n, N);
}
val_t *fft(val_t *buf, size_t input_size, size_t N)
{
// Check if power of two
if ((N & (N - 1)) != 0) {
fprintf(stderr, "FFT size %lu must be power of two\n", N);
return NULL;
}
val_t *tmpbuf = (val_t *) malloc(sizeof(val_t) * N);
// Reverse bits
int least = input_size < N ? input_size : N;
for (int i = 0; i < least; i++) {
index_t reverse = reverse_bits(i, log2(N));
tmpbuf[i] = buf[reverse];
}
// Padding
for (int i = 0; i < (int)N - least; i++) {
tmpbuf[i + least ] = 0;
}
fft_inplace_recur(tmpbuf, 0, N, N);
return tmpbuf;
}
void printhelp(char *prog) {
printf("Usage: %s [options]\n", prog);
puts("Options:");
puts(" -h This help screen");
puts(" -o <FILE> Write output to file");
puts(" -i <FILE> Read from file");
puts(" -f <SIZE> FFT size, must be power of two");
puts("");
printf("FILE should not have more than %d lines, with line seperated values.\n", MAX_FILE_SIZE);
puts("FILE will default to stdin/stdout");
}
int main(int argc, char **argv)
{
int opt;
int optfft = -1;
char *input = NULL;
char *output = NULL;
while ((opt = getopt(argc, argv, "hi:o:f:")) != -1) {
switch(opt) {
case 'o':
output = strdup(optarg);
break;
case 'i':
input = strdup(optarg);
break;
case 'f':
optfft = strtol(optarg, NULL, 10);
break;
case 'h':
default:
printhelp(argv[0]);
return 0;
}
}
if (optfft == -1) {
fprintf(stderr, "FFT not specified\n");
printhelp(argv[0]);
return 1;
}
// Allocate storage
val_t *buf = (val_t *) malloc(sizeof(val_t) * MAX_FILE_SIZE);
if (buf == NULL) {
printf("Could not allocate mega array\n");
return 1;
}
FILE *f = stdin;
if (input != NULL) {
f = fopen(input, "r");
if (f == NULL) {
printf("Could not open file %s\n", input);
return 1;
}
}
double val;
int length;
for (length = 0; fscanf(f, "%lf\n", &val) != EOF; length++) {
buf[length] = (val_t) val;
//printf("Val: %lf + j%lf\n", creal(buf[ii]), cimag(buf[ii]));
}
val_t *res = fft(buf, length, optfft);
if (res == NULL) {
fprintf(stderr, "Error calculating fft\n");
return 1;
}
f = stdout;
if (output != NULL) {
f = fopen(output, "w");
if (f == NULL) {
printf("Could not open file %s\n", input);
return 1;
}
}
for (int ii = 0; ii < optfft; ii++) {
fprintf(f, "%lf%+lfj\n", creal(res[ii]), cimag(res[ii]));
}
}
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