Scalar average

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

#define N 40000000

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

float calc_avg1 (const float array[], int n)
{
    int i;
    float res = 0;
    for (i = 0; i < n; i++) res += array[i];
    return res/n;
}

float calc_avg2 (const float array[], int n)
{
    float a1=0, a2=0, a3=0, a4=0;
    int i;
    for (i=0; i<n; i+=4)
    {
        a1 += array[i];
        a2 += array[i+1];
        a3 += array[i+2];
        a4 += array[i+3];
    }
    return (a1 + a2 + a3 + a4)/n;
}

float calc_avg3 (const float array[], int n)
{
    int i;
    __v4sf r = _mm_set1_ps (0.0);
    for (i=0; i<n; i+=4) r += _mm_load_ps (&(array[i]));
    return (r[0] + r[1] + r[2] + r[3]) / n;
}

int main ()
{
    void *space = malloc (N*sizeof(float)+15);
    float *array = (float*)(((unsigned long)space+15) & ~(unsigned long)15);

    int i;
    double time;
    float avg;

    for (i = 0; i < N; i++) array[i] = 1.0 * random();

    time = gettime();
    avg = calc_avg1 (array, N);
    time = gettime() - time;
    printf ("%f %f\n", time, avg);

    time = gettime();
    avg = calc_avg2 (array, N);
    time = gettime() - time;
    printf ("%f %f\n", time, avg);

    time = gettime();
    avg = calc_avg3 (array, N);
    time = gettime() - time;
    printf ("%f %f\n", time, avg);

    return 0;
}