跨平台的timmer

#ifndef _PERF_TIMER_H_
#define _PERF_TIMER_H_

#ifdef _WIN32
#include <windows.h>
#else
#include <sys/time.h>
#endif

class PerfTimer
{
public:
    PerfTimer();
    ~PerfTimer();

    void reset();
    void start();
    void stop();
    const double duration()const;
    const double duration_milli_seconds()const;
    const double duration_micro_seconds()const;

private:
#ifdef _WIN32
    __int64 m_start_time;
    __int64 m_stop_time;
    __int64 m_freq;
#else
    struct timeval m_start_time;
    struct timeval m_stop_time;
#endif
};

#endif

#include "perftimer.h"

PerfTimer::PerfTimer()
{
#ifdef _WIN32
    QueryPerformanceFrequency((LARGE_INTEGER *)&m_freq);
#endif
    reset();
}

PerfTimer::~PerfTimer()
{
}

/// <summary>
/// resets the timer to ins initial state
/// </summary>
void PerfTimer::reset()
{
#ifdef _WIN32
    m_start_time = 0;
    m_stop_time = 0;
#endif
}

/// <summary>
/// sets the start time of the timer
/// </summary>
void PerfTimer::start()
{
#ifdef _WIN32
    QueryPerformanceCounter((LARGE_INTEGER *)&m_start_time);
#else
    struct timezone tz;
    gettimeofday(&m_start_time, &tz);
#endif
}

/// <summary>
/// Sets the current end time for the timer.  Repeated calls will reset the end time
/// of the timer.
/// </summary>
void PerfTimer::stop()
{
#ifdef _WIN32
    QueryPerformanceCounter((LARGE_INTEGER *)&m_stop_time);
#else
    struct timezone tz;
    gettimeofday(&m_stop_time, &tz);
#endif
}

// Returns the duration of the timer (in seconds)

const double PerfTimer::duration()const
{
#ifdef _WIN32
    return (double)(m_stop_time - m_start_time) / (double)m_freq;
#else
    return (double)m_stop_time.tv_sec - (double)m_start_time.tv_sec +
        (((double)m_stop_time.tv_usec - (double)m_start_time.tv_usec)/1000000.0);
#endif
}

const double PerfTimer::duration_milli_seconds()const
{
#ifdef _WIN32
    return ((double)(m_stop_time - m_start_time) / (double)m_freq) * 1000;
#else
    return ((double)m_stop_time.tv_sec - (double)m_start_time.tv_sec) * 1000.0 +
        (((double)m_stop_time.tv_usec - (double)m_start_time.tv_usec)/1000.0);
#endif
}

const double PerfTimer::duration_micro_seconds()const
{
#ifdef _WIN32
    return ((double)(m_stop_time - m_start_time) / (double)m_freq) * 1000 * 1000;
#else
    return ((double)m_stop_time.tv_sec - (double)m_start_time.tv_sec) * 1000000.0 +
        ((double)m_stop_time.tv_usec - (double)m_start_time.tv_usec);
#endif
}