4.17. TimerCountdown CLASS
	  TimerCountdown class helps to keep track of the 
	  time spent in a function. This class subtracts the time elapsed between 
	  instantiation and destruction time from the timeval argument passed
	  to its constructor. 
	
4.17.1. DESCRIPTION
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class TimerCountdown
{
public:
    TimerCountdown (TimeVal* wait_time_);
    ~TimerCountdown ();
};
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4.17.2. USAGE
For example, if we want to know how much time is spent
		in a function call, then following can be employed:
	  
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void sluggard (TimeVal* tv_)
{
    TimerCountdown traceTime (tv_);
    // do time-intensive calculation ...
}
void foo ()
{
    TimeVal time_spent (60, 0);   // 60 seconds
    sluggard (&time_spent);
    cout << "Time remaining: " << TimeVal.fmtString();
}
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