[boost] max elapsed time of boost::timer

From: Toon Knapen (toon.knapen_at_[hidden])
Date: 2004-04-21 07:37:37

The documentation of boost::timer states that 'The maximum measurable 
elapsed time may be as low as 596.5 hours (or even less) ...'.

Well on many 32bit platforms this would probably even be about 71 hours.
Apparantly POSIX requires CLOCKS_PER_SEC to be 10e6, so if clock_t is 32 
bit, the maximum of ( clock() / CLOCKS_PER_SEC ) is 4294 seconds.

Because accuracy for clock() is generally about 1 sec, using clock() is 
not very usefull for doing timings of short (in time) events. Even more, 
for short events, the boost::timer might also influence the timing too 
much. So clock() is generally interesting for longer timings (from 10 
sec onwards).

But for long events the clock_t wraps around too fast (as mentioned 
above). And if you're unlucky that you _start_time = clock() is or a bit 
smaller than std::numeric_limits< clock_t >::max() (thus near the 
wrap-around point), directly afterwards the expression 'clock() - start' 
will result in a negative value.

So I would like to suggest for boost::timer to use std::time_t and use 
std::time(NULL) instead of clock() and use std::difftime to calculate 
the elapsed time.

toon