[Pierre-Marie Baty]

Nevermind, found it - in limits.h

Here's the function now.

float ProcessTime (void)
{
   // this function returns the time in seconds elapsed since the executable process started.
   // The rollover check ensures the program will continue running after clock() will have
   // overflown its integer value (it does so every 24 days or so). With this rollover check
   // we have a lifetime of more than billion years, w00t!
   // thanks to botmeister for the rollover check idea.
 
   static long current_clock;
   static long prev_clock = 0;
   static long rollover_count = 0;
   static double time_in_seconds;
   static double rollover = ((double) LONG_MAX + 1) / CLOCKS_PER_SEC; // fixed, won't move
   
   current_clock = clock (); // get system clock
 
   // has the clock overflown ?
   if (current_clock < prev_clock)
	  rollover_count++; // omg, it has, we're running for more than 24 days!
 
   // now convert the time to seconds since last rollover
   time_in_seconds = (double) current_clock / CLOCKS_PER_SEC; // convert clock to seconds
 
   prev_clock = current_clock; // keep track of current time for future calls of this function
 
   // and return the time in seconds, adding the overflow differences if necessary.
   return (time_in_seconds + rollover * rollover_count);
}