#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <math.h>
#include "x86intrin.h"

struct rolling_stddev
{
    uint64_t sum, count;
    float mean, m2;
};

void roll(struct rolling_stddev *r, uint64_t value)
{
    r->count++;
    r->sum += value;
    float d = value-r->mean;
    r->mean += d/r->count;
    r->m2 += d*(value-r->mean);
}

float dev(struct rolling_stddev *r)
{
    return (r->m2/(r->count-1));
}

void test_clock(const char *name, clockid_t clockid)
{
    struct rolling_stddev d = { 0 };
    struct timespec ts, tp, te;
    clock_gettime(clockid, &ts);
    te = ts;
    for (int i = 0; i < 100000000; i++)
    {
        clock_gettime(clockid, &tp);
        uint64_t cur = ((tp.tv_sec-te.tv_sec)*1000000000 + (tp.tv_nsec-te.tv_nsec));
        roll(&d, cur);
        te = tp;
    }
    printf("%s: %lu ns, stddev %.2f ns\n", name, (te.tv_sec-ts.tv_sec)*10 + (te.tv_nsec-ts.tv_nsec)/100000000, sqrt(dev(&d)));
}

void test_rdtsc()
{
    struct timespec ts, te;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    uint64_t s = __rdtsc(), e;
    for (int i = 0; i < 100000000; i++)
    {
        e = __rdtsc();
    }
    clock_gettime(CLOCK_MONOTONIC, &te);
    printf("RDTSC: %lu ns\n", (te.tv_sec-ts.tv_sec)*10 + (te.tv_nsec-ts.tv_nsec)/100000000);
}

int main(int narg, char **args)
{
    test_rdtsc();
    test_clock("CLOCK_MONOTONIC_RAW", CLOCK_MONOTONIC_RAW);
    test_clock("CLOCK_MONOTONIC", CLOCK_MONOTONIC);
    test_clock("CLOCK_MONOTONIC_COARSE", CLOCK_MONOTONIC_COARSE);
    test_clock("CLOCK_REALTIME", CLOCK_REALTIME);
    test_clock("CLOCK_REALTIME_COARSE", CLOCK_REALTIME_COARSE);
    return 0;
}