//  posix_2001_cpu_timer.hpp 

//  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_POSIX_2001_CPU_TIMER_HPP
#define BOOST_POSIX_2001_CPU_TIMER_HPP

#include <boost/typeof/typeof.hpp>  // BOOST_TYPEOF

namespace boost {
namespace detail {          

namespace {
#include <sys/times.h>
#include <sys/resource.h>
} // to not pollute ::boost::detail by symbols defined in the above headers

class cpu_timer_impl  // implementation of cpu_timer
{
private:
  typedef struct rusage CPUclock; // kernel, user
  CPUclock start_clock_; 
  
  static const size_t clock_per_sec_ = 1000000; 
  // 1 us = 1/millionths of a second
  static const CPUclock get_cpu_time();

public:
  cpu_timer_impl();  // sets cpu() to zero
  void   restart();  // resets cpu() to zero
  double cpu() const;   // returns CPU time in seconds
  double cpu_max() const;  // maximum possible value for cpu()
  double cpu_min() const   // minimum possible value for cpu()
  { return double(1)/double(clock_per_sec_); }
   
}; // cpu_timer_impl


inline
const cpu_timer_impl::CPUclock cpu_timer_impl::get_cpu_time()
{
  CPUclock current_clock;
  
  getrusage(RUSAGE_SELF, & current_clock );
  
  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 // maximum possible value for cpu()
{
  typedef BOOST_TYPEOF(start_clock_.ru_utime.tv_sec) ru_uint;
  return  double( (::std::numeric_limits<ru_uint>::max)()
                   - start_clock_.ru_utime.tv_sec   // seconds
                   - start_clock_.ru_stime.tv_sec )
	      - (   double(start_clock_.ru_utime.tv_usec) // microseconds
            + double(start_clock_.ru_stime.tv_usec) )
          / double(clock_per_sec_); 
}

inline
double cpu_timer_impl::cpu() const
{ 
  const CPUclock current_clock = get_cpu_time();
  
  return  (  double( current_clock.ru_utime.tv_usec )       // microseconds
           - double( start_clock_.ru_utime.tv_usec )   // avoid substraction 
           + double( current_clock.ru_stime.tv_usec )  // of unsigned:     
           - double( start_clock_.ru_stime.tv_usec ) ) // may wrap around!
         / clock_per_sec_
        + double(  current_clock.ru_utime.tv_sec            // seconds
                 - start_clock_.ru_utime.tv_sec )  // with whole seconds 
        + double(  current_clock.ru_stime.tv_sec   // the substraction 
                 - start_clock_.ru_stime.tv_sec ); // is not dangerous
                                                   // because counters do not
                                                   // wrap around on overflow
}

}} // namespace boost::detail

#endif  // BOOST_POSIX_2001_CPU_TIMER_HPP guard