cosatan and sinatan performance benchmark

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

#include <sys/time.h>
#include <time.h>

#define MAX 100000
double A[MAX];

static double sinatan(double x)
{
    return sin(atan(x));
}

static double cosatan(double x)
{
    return cos(atan(x));
}

static double sinatan2(double x)
{
    return x / sqrt(x*x + 1);
}

static double cosatan2(double x)
{
    return 1./ sqrt(x*x + 1);
}


static void generate_random_array(int n, double a[])
{
    int i;

    for (i = 0; i < n; ++i)
        a[i] = (double) rand() / (double) RAND_MAX;
}

int main()
{
    struct timespec start, end;
    unsigned long long int delta_t;
    int i, j;
    volatile double y;

    generate_random_array(MAX, A);


    //Initialize timespec structures.
    clock_gettime(CLOCK_MONOTONIC_RAW, &start);
    clock_gettime(CLOCK_MONOTONIC_RAW, &end);

    clock_gettime(CLOCK_MONOTONIC_RAW, &start);
    for (i = 0; i < MAX; ++i)
    {
        y = sinatan2(A[i]);
    }
    clock_gettime(CLOCK_MONOTONIC_RAW, &end);
    delta_t = end.tv_nsec - start.tv_nsec;
    printf("time x/sqrt(x*x + 1) = %llu\n", delta_t);

    clock_gettime(CLOCK_MONOTONIC_RAW, &start);
    for (i = 0; i < MAX; ++i)
    {
        y = sinatan(A[i]);
    }
    clock_gettime(CLOCK_MONOTONIC_RAW, &end);
    delta_t = (end.tv_nsec - start.tv_nsec);
    printf("time sin(atan(x))    = %llu\n", delta_t);

    clock_gettime(CLOCK_MONOTONIC_RAW, &start);
    for (i = 0; i < MAX; ++i)
    {
        y = cosatan2(A[i]);
    }
    clock_gettime(CLOCK_MONOTONIC_RAW, &end);
    delta_t = end.tv_nsec - start.tv_nsec;
    printf("time 1/sqrt(x*x + 1) = %llu\n", delta_t);

    clock_gettime(CLOCK_MONOTONIC_RAW, &start);
    for (i = 0; i < MAX; ++i)
    {
        y = cosatan(A[i]);
    }
    clock_gettime(CLOCK_MONOTONIC_RAW, &end);
    delta_t = (end.tv_nsec - start.tv_nsec);
    printf("time cos(atan(x))    = %llu\n", delta_t);

    return 0;
}