atan2 vs acos benchmark

#include <iostream>
#include <vector>
#include <cmath>
#include <cstdlib>

#include "TimeET.h"
// TimeET from Tekkotsu library:
// http://hg.tekkotsu.org/Tekkotsu/raw-file/tip/Shared/TimeET.h
// http://hg.tekkotsu.org/Tekkotsu/raw-file/tip/Shared/TimeET.cc

using namespace std;
float randf() { return random()/(float)((1U<<31)-1); }

int main(int argc, char** argv) {
    const size_t COUNT=1<<25;
    vector<float> n(COUNT+1);
    for(size_t i=0; i<COUNT+1; ++i)
        n[i]=randf()*2*M_PI-M_PI;

    vector<float> o(COUNT);
    TimeET ot;
    for(size_t i=0; i<COUNT; ++i)
        o[i] = 0;
    ot=ot.Age();
    cout << "overhead: " << ot.Value()/COUNT*1e9 << endl;

    vector<float> r1(COUNT);
    TimeET at2;
    for(size_t i=0; i<COUNT; ++i)
        r1[i] = atan2(n[i],n[i+1]);
    cout << "atan2: " << (at2.Age()-ot).Value()/COUNT*1e9 << endl;

    vector<float> r2(COUNT);
    TimeET ac;
    for(size_t i=0; i<COUNT; ++i)
        r2[i] = acos(n[i]);
    cout << "acos: " << (ac.Age()-ot).Value()/COUNT*1e9 << endl;

    vector<float> r3(COUNT);
    TimeET acd;
    for(size_t i=0; i<COUNT; ++i)
        r3[i] = acos(n[i]/n[i+1]);
    cout << "acos/: " << (acd.Age()-ot).Value()/COUNT*1e9 << endl;

    vector<float> r4(COUNT);
    TimeET at;
    for(size_t i=0; i<COUNT; ++i)
        r4[i] = atan(n[i]);
    cout << "atan: " << (at.Age()-ot).Value()/COUNT*1e9 << endl;

    vector<float> r5(COUNT);
    TimeET atd;
    for(size_t i=0; i<COUNT; ++i)
        r5[i] = atan(n[i]/n[i+1]);
    cout << "atan/: " << (atd.Age()-ot).Value()/COUNT*1e9 << endl;

}