High speed timer

hstimer.hpp

#pragma once

#include <ctime>
#include <cstdint>
#include <iostream>
#include <rte_cycles.h>

class HighSpeedTimer {
public:
        std::uint64_t
        nanoseconds_since_epoch()
        {
            auto cur_tsc = rdtsc();
            uint64_t rs{};
            if (cur_tsc - prev_tsc_ > 20'000 || cur_tsc < prev_prev_tsc_ || prev_prev_ts_.tv_sec == 0)
            {
                prev_prev_tsc_ = prev_tsc_;
                prev_prev_ts_ = prev_ts_;
                clock_gettime(CLOCK_REALTIME, &prev_ts_);
                prev_tsc_ =  cur_tsc;
                cycle_duration = float((prev_ts_.tv_sec - prev_prev_ts_.tv_sec)*1'000'000'000
                                            + (prev_ts_.tv_nsec - prev_prev_ts_.tv_nsec))/(prev_tsc_ - prev_prev_tsc_);
                rs = prev_ts_.tv_sec * 1'000'000'000;
                rs += prev_ts_.tv_nsec;
            }
            else
            {
                rs = prev_ts_.tv_sec*1'000'000'000;
                rs += prev_ts_.tv_nsec;
                rs += (uint64_t)(cycle_duration*(cur_tsc - prev_tsc_));
            }
            return rs;
        }

private:
        uint64_t rdtsc() {
            union {
                uint64_t tsc_64;
                struct {
                    uint32_t lo_32;
                    uint32_t hi_32;
                };
            } tsc;

            asm volatile("rdtsc" : "=a" (tsc.lo_32), "=d" (tsc.hi_32));
            return tsc.tsc_64;
        }
        uint64_t prev_tsc_{};
        uint64_t prev_prev_tsc_{};
        struct timespec prev_ts_{};
        struct timespec prev_prev_ts_{};
        float cycle_duration{};
};