/*
 * benchmark.h
 * Simple benchmarking routines for C++11
 *
 * Andy Clifton
 * August, 2016
 */

#ifndef _BENCHMARK_H_
#define _BENCHMARK_H_

#include <time.h> // for clock_gettime
#include <memory> // for std::unique_ptr

// Types for markers and durations
using marker_t = long long;
using duration_t = long double;


/* start_timing()
 * Returns a marker value that can later be used to accurately determine the
 * time taken by a computation.
 */
inline marker_t start_timing() {
    std::unique_ptr<timespec> ts{new timespec}; 

    // It's debatable whether we want CLOCK_PROCESS_CPUTIME_ID or 
    // CLOCK_MONOTONIC. The process clock has the advantage that it does not
    // include time spent running *other* processes, so if the system is under
    // load, it will be unaffected. However, it also does not include time
    // spent executing syscalls, such as for I/O. So doing things like reading
    // in a huge file will not be counted, even though we would expect that
    // that time would be measured.

    if(clock_gettime(CLOCK_MONOTONIC, ts.get()) == 0) {
        return ts->tv_nsec;
    }
    else
        return 0;
}


/* get_elapsed_time(start)
 * Returns the number of seconds elapsed since the starting time (as returned
 * by start_timing()).
 *
 * start:   Starting time to measure the duration since.
 * Returns: elapsed time in seconds since start, or 0 on error.
 */
inline duration_t get_elapsed_time(marker_t start) {
    long long now = start_timing(); // Get current time

    return (1.0 * now - start) / 1000000000L; // convert from nanoseconds to sec
}

#endif