Vector average

#include <sys/time.h>
#include <sys/param.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <xmmintrin.h>

typedef float dot[4];
#define N 100000000

double gettime ()
{
    struct timeval tv;
    gettimeofday (&tv, 0);
    return (double)tv.tv_sec + (0.000001 * (double)tv.tv_usec);
}

void calc_avg1 (dot res, const dot array[], int n)
{
    int i,j;
    memset (res, 0, sizeof (dot));
    for (i = 0; i < n; i++)
    {
        for (j = 0; j<4; j++) res[j] += array[i][j];
    }
    for (j = 0; j<4; j++) res[j] /= n;
}

void calc_avg2 (dot res, const dot array[], int n)
{
    int i;
    __v4sf r = _mm_set1_ps (0.0);
    for (i=0; i<n; i++) r += _mm_load_ps (array[i]);
    r /= _mm_set1_ps ((float)n);
    _mm_store_ps (res, r);
}

int main ()
{
    void *space = malloc (N*sizeof(dot)+15);
    dot *array = (dot*)(((unsigned long)space+15) & ~(unsigned long)15);
    dot avg __attribute__((aligned(16)));
    int i;
    double time;

    for (i = 0; i < N; i++)
    {
        array[i][0] = 1.0*random();
        array[i][1] = 1.0*random();
        array[i][2] = 1.0*random();
    }
    time = gettime();
    calc_avg1 (avg, array, N);
    time = gettime() - time;
    printf ("%f\n%f %f %f\n", time, avg[0], avg[1], avg[2]);

    time = gettime();
    calc_avg2 (avg, array, N);
    time = gettime() - time;
    printf ("%f\n%f %f %f\n", time, avg[0], avg[1], avg[2]);
    return 0;
}