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/*
fftbench.c
Written by Scott Robert Ladd (scott@coyotegulch.com)
No rights reserved. This is public domain software, for use by anyone.
A number-crunching benchmark using LUP-decomposition to solve a large
linear equation.
The code herein is design for the purpose of testing computational
performance; error handling is minimal.
In fact, this is a weak implementation of the FFT; unfortunately, all
of my really nifty FFTs are in commercial code, and I haven't had time
to write a new FFT routine for this benchmark. I may add a Hartley
transform to the seat, too.
Actual benchmark results can be found at:
http://scottrobertladd.net/coyotegulch/
Please do not use this information or algorithm in any way that might
upset the balance of the universe or otherwise cause a disturbance in
the space-time continuum.
*/
#include <time.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include "fftbench.h"
// embedded random number generator; ala Park and Miller
static long seed = 1325;
static const long IA = 16807;
static const long IM = 2147483647;
static const double AM = 4.65661287525E-10;
static const long IQ = 127773;
static const long IR = 2836;
static const long MASK = 123459876;
static double random_double()
{
long k;
double result;
seed ^= MASK;
k = seed / IQ;
seed = IA * (seed - k * IQ) - IR * k;
if (seed < 0)
seed += IM;
result = AM * seed;
seed ^= MASK;
return result;
}
static const int N = 100;
static const int NM1 = 99; // N - 1
static const int NP1 = 101; // N + 1
static void lup_decompose(FFTBench *fftbench)
{
int i, j, k, k2, t;
double p, temp, **a;
int *perm = (int *) malloc(sizeof(double) * N);
fftbench->p = perm;
a = fftbench->a;
for (i = 0; i < N; ++i)
perm[i] = i;
for (k = 0; k < NM1; ++k) {
p = 0.0;
for (i = k; i < N; ++i) {
temp = fabs(a[i][k]);
if (temp > p) {
p = temp;
k2 = i;
}
}
// check for invalid a
if (p == 0.0)
return;
// exchange rows
t = perm[k];
perm[k] = perm[k2];
perm[k2] = t;
for (i = 0; i < N; ++i) {
temp = a[k][i];
a[k][i] = a[k2][i];
a[k2][i] = temp;
}
for (i = k + 1; i < N; ++i) {
a[i][k] /= a[k][k];
for (j = k + 1; j < N; ++j)
a[i][j] -= a[i][k] * a[k][j];
}
}
}
static double *lup_solve(FFTBench *fftbench)
{
int i, j, j2;
double sum, u;
double *y = (double *) malloc(sizeof(double) * N);
double *x = (double *) malloc(sizeof(double) * N);
double **a = fftbench->a;
double *b = fftbench->b;
int *perm = fftbench->p;
for (i = 0; i < N; ++i) {
y[i] = 0.0;
x[i] = 0.0;
}
for (i = 0; i < N; ++i) {
sum = 0.0;
j2 = 0;
for (j = 1; j <= i; ++j) {
sum += a[i][j2] * y[j2];
++j2;
}
y[i] = b[perm[i]] - sum;
}
i = NM1;
while (1) {
sum = 0.0;
u = a[i][i];
for (j = i + 1; j < N; ++j)
sum += a[i][j] * x[j];
x[i] = (y[i] - sum) / u;
if (i == 0)
break;
--i;
}
free(y);
return x;
}
FFTBench *fft_bench_new(void)
{
FFTBench *fftbench;
int i, j;
fftbench = g_new0(FFTBench, 1);
// generate test data
fftbench->a = (double **) malloc(sizeof(double *) * N);
for (i = 0; i < N; ++i) {
fftbench->a[i] = (double *) malloc(sizeof(double) * N);
for (j = 0; j < N; ++j)
fftbench->a[i][j] = random_double();
}
fftbench->b = (double *) malloc(sizeof(double) * N);
for (i = 0; i < N; ++i)
fftbench->b[i] = random_double();
return fftbench;
}
void fft_bench_run(FFTBench *fftbench)
{
lup_decompose(fftbench);
double *x = lup_solve(fftbench);
free(x);
}
void fft_bench_free(FFTBench *fftbench)
{
int i;
// clean up
for (i = 0; i < N; ++i)
free(fftbench->a[i]);
free(fftbench->a);
free(fftbench->b);
free(fftbench->p);
free(fftbench->r);
g_free(fftbench);
}
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