timer.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public License,
 * v. 2.0. If a copy of the MPL was not distributed with this file, You can
 * obtain one at http://mozilla.org/MPL/2.0/.
 * 
 * 
 * Copyright (c) 2016, Lutz, Clemens <lutzcle@cml.li>
 */

#ifndef TIMER_HPP_
#define TIMER_HPP_

#include <cstdint>
#include <chrono>

// Check if we are using the syscall, as it is slow
// We want to use clock_gettime()
// If it doesn't work, try setting CPP_FLAGS "--enable-libstdcxx-time=yes"
// This enables link-time checking for clock_gettime() in GCC/G++
// Checks taken from https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63400#c1
#ifdef _GLIBCXX_USE_CLOCK_REALTIME
#ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
#warning system_clock using syscall(SYS_clock_gettime, CLOCK_REALTIME, &tp);
#else
//#warning system_clock using clock_gettime(CLOCK_REALTIME, &tp);
#endif
#elif defined(_GLIBCXX_USE_GETTIMEOFDAY)
#warning system_clock using gettimeofday(&tv, 0);
#else
#warning system_clock using std::time(0);
#endif

#ifdef _GLIBCXX_USE_CLOCK_MONOTONIC
#ifdef _GLIBCXX_USE_CLOCK_GETTIME_SYSCALL
#warning steady_clock using syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &tp);
#else
//#warning steady_clock using clock_gettime(CLOCK_MONOTONIC, &tp);
#endif
#else
#warning steady_clock using time_point(system_clock::now().time_since_epoch());
#endif

namespace Timer {

// Timer for benchmarking
// Header-only implementation for compiler inlining
// Verified that G++ with -O2 optimization inlines these functions
class Timer {
public:
    void start() {
        start_epoch_ = std::chrono::steady_clock::now();
    }

    template <typename UnitT = std::chrono::nanoseconds>
    uint64_t stop() {
        std::chrono::steady_clock::time_point stop_epoch;
        UnitT time_span;

        stop_epoch = std::chrono::steady_clock::now();
        time_span = std::chrono::duration_cast<UnitT>(stop_epoch - start_epoch_);
        return time_span.count();
    }

private:
    std::chrono::steady_clock::time_point start_epoch_;
};

}

#endif /* TIMER_HPP_ */