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# 6 Source Code Presentation

```#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <sys/time.h>

#define PI 3.14159265359
#define MAXPOW 24

struct complex
{
double r;
double i;
};

int pow_2[MAXPOW];
int pow_4[MAXPOW];

void twiddle(struct complex *W, int N, double stuff)
{
W->r=cos(stuff*2.0*PI/(double)N);
W->i=-sin(stuff*2.0*PI/(double)N);
}

void bit_reverse_reorder(struct complex *W, int N)
{
int bits, i, j, k;
double tempr, tempi;

for (i=0; i<MAXPOW; i++)
if (pow_2[i]==N) bits=i;

for (i=0; i<N; i++)
{
j=0;
for (k=0; k<bits; k++)
if (i&pow_2[k]) j+=pow_2[bits-k-1];

if (j>i)  /** Only make "up" swaps */
{
tempr=W[i].r;
tempi=W[i].i;
W[i].r=W[j].r;
W[i].i=W[j].i;
W[j].r=tempr;
W[j].i=tempi;
}
}
}
void bit_r4_reorder(struct complex *W, int N)
{
int bits, i, j, k;
double tempr, tempi;

for (i=0; i<MAXPOW; i++)
if (pow_2[i]==N) bits=i;

for (i=0; i<N; i++)
{
j=0;
for (k=0; k<bits; k+=2)
{
if (i&pow_2[k]) j+=pow_2[bits-k-2];
if (i&pow_2[k+1]) j+=pow_2[bits-k-1];
}

if (j>i)  /** Only make "up" swaps */
{
tempr=W[i].r;
tempi=W[i].i;
W[i].r=W[j].r;
W[i].i=W[j].i;
W[j].r=tempr;
W[j].i=tempi;
}
}
}

void radix4(struct complex *x, int N)
{
int    n2, k1, N1, N2;
struct complex W, bfly[4];

N1=4;
N2=N/4;

/** Do 4 Point DFT */
for (n2=0; n2<N2; n2++)
{
/** Don't hurt the butterfly */
bfly[0].r = (x[n2].r + x[N2 + n2].r + x[2*N2+n2].r + x[3*N2+n2].r);
bfly[0].i = (x[n2].i + x[N2 + n2].i + x[2*N2+n2].i + x[3*N2+n2].i);

bfly[1].r = (x[n2].r + x[N2 + n2].i - x[2*N2+n2].r - x[3*N2+n2].i);
bfly[1].i = (x[n2].i - x[N2 + n2].r - x[2*N2+n2].i + x[3*N2+n2].r);

bfly[2].r = (x[n2].r - x[N2 + n2].r + x[2*N2+n2].r - x[3*N2+n2].r);
bfly[2].i = (x[n2].i - x[N2 + n2].i + x[2*N2+n2].i - x[3*N2+n2].i);

bfly[3].r = (x[n2].r - x[N2 + n2].i - x[2*N2+n2].r + x[3*N2+n2].i);
bfly[3].i = (x[n2].i + x[N2 + n2].r - x[2*N2+n2].i - x[3*N2+n2].r);

/** In-place results */
for (k1=0; k1<N1; k1++)
{
twiddle(&W, N, (double)k1*(double)n2);
x[n2 + N2*k1].r = bfly[k1].r*W.r - bfly[k1].i*W.i;
x[n2 + N2*k1].i = bfly[k1].i*W.r + bfly[k1].r*W.i;
}
}

/** Don't recurse if we're down to one butterfly */
if (N2!=1)
for (k1=0; k1<N1; k1++)
{
}
}

void radix2(struct complex *data, int N)
{
int    n2, k1, N1, N2;
struct complex W, bfly[2];

N1=2;
N2=N/2;

/** Do 2 Point DFT */
for (n2=0; n2<N2; n2++)
{
/** Don't hurt the butterfly */
twiddle(&W, N, (double)n2);
bfly[0].r = (data[n2].r + data[N2 + n2].r);
bfly[0].i = (data[n2].i + data[N2 + n2].i);
bfly[1].r = (data[n2].r - data[N2 + n2].r) * W.r -
((data[n2].i - data[N2 + n2].i) * W.i);
bfly[1].i = (data[n2].i - data[N2 + n2].i) * W.r +
((data[n2].r - data[N2 + n2].r) * W.i);

/** In-place results */
for (k1=0; k1<N1; k1++)
{
data[n2 + N2*k1].r = bfly[k1].r;
data[n2 + N2*k1].i = bfly[k1].i;
}
}

/** Don't recurse if we're down to one butterfly */
if (N2!=1)
for (k1=0; k1<N1; k1++)
}

void main(int argc, char *argv[])
{
FILE   *infile;
int    i;
struct complex *data;
double freq, phase, fs, A;
int    dotime;
struct timeval start, end;
long   totaltime;

#ifdef GEN
if (argc!=9)
{
printf("usage:\n");
printf("    fft [A] [f] [phase] [fs] [num samp] [sequence length] [radix] [time]\n");
printf("        output: DFT\n");
exit(1);
}

sscanf(argv[1], "%lf", &A);
sscanf(argv[2], "%lf", &freq);
sscanf(argv[3], "%lf", &phase);
sscanf(argv[4], "%lf", &fs);
sscanf(argv[5], "%d", &numsamp);
sscanf(argv[6], "%d", &N);
sscanf(argv[8], "%d", &dotime);
#endif
#ifndef GEN
if (argc<4)
{
printf("usage:\n");
printf("    fft [input file] [sequence length] [radix]\n");
printf("        output: DFT\n");
exit(1);
}
else if ((infile=fopen(argv[1], "r"))==NULL)
{
printf("Error reading input sequence file: %s\n", argv[1]);
exit(1);
}

sscanf(argv[2], "%d", &N);
dotime=0;
#endif

/** Set up power of two arrays */
pow_2[0]=1;
for (i=1; i<MAXPOW; i++)
pow_2[i]=pow_2[i-1]*2;
pow_4[0]=1;
for (i=1; i<MAXPOW; i++)
pow_4[i]=pow_4[i-1]*4;

if ((data=malloc(sizeof(struct complex)*(size_t)N))==NULL)
{
fprintf(stderr, "Out of memory!\n");
exit(1);
}

/** Generate cosine **/
#ifdef GEN
for (i=0; i<N; i++)
{
data[i].r=0.0;
data[i].i=0.0;
}
for (i=0; i<numsamp; i++)
data[i].r=A*cos(2.0*PI*freq*i/fs - phase*PI/180);
#endif
#ifndef GEN
for (i=0; i<N; i++)
{
fscanf(infile, "%lf", &data[i].r);
data[i].i=0.0;
}
#endif

gettimeofday(&start, (struct timezone *) 0);
gettimeofday(&end, (struct timezone *) 0);
totaltime=(end.tv_sec*1000000 + end.tv_usec)-(start.tv_sec*1000000
+ start.tv_usec);

if (!dotime)
for (i=0; i<N; i++)
printf("%f\n", sqrt(data[i].r*data[i].r +
data[i].i*data[i].i));
else
printf("%ld us\n\n", totaltime);

#ifndef GEN
fclose(infile);
#endif
}
```

Mike Andrews
6/29/1998