//  ms_windows_cpu_timer.hpp header file

//  Copyright by Yuriy Koblents-Mishke, 2007.  
//  Distributed under the Boost Software License, Version 1.0. 
//  (See accompanying file LICENSE_1_0.txt 
//  or copy at http://www.boost.org/LICENSE_1_0.txt)

// ???  //  See http://www.???????   for documentation.

#ifndef BOOST_MS_WINDOWS_CPU_TIMER_HPP
#define BOOST_MS_WINDOWS_CPU_TIMER_HPP

// MS Windows is so widespread that it deserves a native implementation 

#include <limits>
#include <utility> // pair
// ?? #include <boost/utility.hpp>
#include <boost/typeof/typeof.hpp>  // BOOST_TYPEOF

namespace boost {
namespace detail {          


namespace {
#include <windows.h>
} // avoids pollution of ::boost::detail by symbols defined in windows.h

struct cpu_timer_impl  // implementation of cpu_timer
{
public:
  cpu_timer_impl();  // sets cpu to 0

  void   restart(); // resets cpu() to 0
  double cpu() const;                  // return cpu time in seconds
  double cpu_max() const;   // return the maximum possible value for cpu()

  double cpu_min() const    // return the minimum possible value for cpu()
  { return double(1)/double(clock_per_sec_); }
   
private:
  typedef std::pair< __int64, __int64 > CPUclock; // kernel, user
  CPUclock start_clock_; // CPU clock on the moment when timing started
  
  static const __int64 clock_per_sec_ = 10000000; // 100 nanoseconds
  static const CPUclock get_cpu_time();
}; // cpu_timer_impl


inline
const cpu_timer_impl::CPUclock cpu_timer_impl::get_cpu_time()
{
  // Attention:   
  // It was tested only on on Windows 2000 Pro and Windows XP Pro.
  // I expect it to work also on all versions of Windows Vista, 
  // Windows Server "Longhorn", Windows Server 2003, Windows 2000 Server, 
  // Windows XP Home and other versions of Windows XP, 
  // Windows NT (Workstation and Server), version 3.5 and later,
  // and on many implementations of Windows CE, version 2.12 and later.
  // !!! The current implementation will not work on Windows 95 / 98 / ME !!!

  // Reasons: 
  //   The implementation uses function GetThreadTimes
  // described in Microsoft documentation available on the following websites
  // http://msdn2.microsoft.com/en-us/library/ms683237.aspx
  // http://msdn2.microsoft.com/en-us/library/ms908464.aspx
  //   See also an useful discussion on a Microsoft forum
  // http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=990282&SiteID=1
  
  // According to the Microsoft documentation, GetThreadTimes is supported  
  // on Windows NT, starting from ver. 3.51, and its descendants
  // including all versions of Windows 2000, Windows XP, Windows Vista, and
  // Windows Server 2003.
  
  // Windows CE, strating from versions 3.0 or even 2.12, also supports 
  // this function, but vendors can remove it from vendor-specific builds.
  
  // The function is not supported on Windows 95 / 98 / ME
  
  
  CPUclock current_clock;
  
  FILETIME dummy1, dummy2;
  GetThreadTimes( GetCurrentThread(), 
                  &dummy1, &dummy2, 
                  (FILETIME*)&current_clock.first, 
                  (FILETIME*)&current_clock.second );
                  
  return current_clock;
}

inline
cpu_timer_impl::cpu_timer_impl() : start_clock_( get_cpu_time() ){}

inline
void cpu_timer_impl::restart()
{
  start_clock_ = get_cpu_time(); 
}

inline
double cpu_timer_impl::cpu_max() const   // return estimated maximum value for cpu()
{
  return double( (::std::numeric_limits< __int64 >::max)()
                  - start_clock_.first - start_clock_.second) 
     / double(clock_per_sec_); 
}


inline
double cpu_timer_impl::cpu() const
{ 
  const CPUclock current_clock = get_cpu_time();
  
  // calculates CPU times as a difference of current ans saved CPU "clocks"
  // adds CPU time spent in user code and in kernel in behalf of user
  return  double( ( current_clock.first - start_clock_.first ) + 
                  ( current_clock.second - start_clock_.second ) ) 
        / double( clock_per_sec_ ); 
}

}} // namespace boost::detail

#endif  // BOOST_MS_WINDOWS_CPU_TIMER_HPP guard