RE: [boost] [named_params] timing trivia and some comments

From: Matthew Hurd (matt_at_[hidden])
Date: 2004-03-03 08:53:35

> On Behalf Of Matthew Hurd
> Subject: [boost] [named_params] timing trivia and some comments
> 
> Been looking at the very cute named_params in the sandbox.  Getting around
> to trying to do some stuff with it.
> 
> Noticed something interesting w.r.t. vc7.1 optimization:
> 
> BOOST_NAMED_PARAMS_FUN(double, power, 0, 2, power_keywords )
> {
> 	double b = p[base | 10];
> 	double e = p[exponent | 1];
> 	return pow(b ,e);
> }
> 
> double pow_wrap(double b, double e)
> {
> 	return pow(b,e);
> }
> 
> are the same speed, around 25 nanoseconds on my machine, when called with
> some variable parameters (	now = pow_wrap(t.elapsed(),t.elapsed() /
> (rand() * t.elapsed())); )
> to defeat the chance of variable elimination and constant propagation.
> 
> But interestingly,
> 
> BOOST_NAMED_PARAMS_FUN(double, power, 0, 2, power_keywords )
> {
> 	return pow(p[base | 10] , p[exponent | 1]);
> }
> 
> is more than five times slower at 144 nanoseconds.

FWIW,

        Calling

        power(exponent = t.elapsed() / (rand() * t.elapsed()), base=
t.elapsed() );

That is, with the parameters in the reverse order to the natural order,
takes nearly twice as long with this configuration, so there seems a little
penalty for being out of order with this example, compiler, hardware and OS.
Not sure it means anything much though.

Regards,

Matt Hurd.

________________________________________
----------------------------------------------------------------------------
----
                        looper invasive timing estimate
                               simple_named_params
----------------------------------------------------------------------------
----
median time = 52.15311004785687 nanoseconds
90% range size = 0.4784688995215372 nanoseconds
widest range size (max - min) = 10.32153110047848 microseconds
minimum time = 46.41148325358853 nanoseconds
maximum time = 10.36794258373207 microseconds
50% range = (52.15311004785686 nanoseconds, 52.15311004785688 nanoseconds)
50% range size = 3.308722450212111e-014 nanoseconds
----------------------------------------------------------------------------
----
                        looper invasive timing estimate
                                   simple_wrap
----------------------------------------------------------------------------
----
median time = 24.88038277512962 nanoseconds
90% range size = 3.308722450212111e-015 nanoseconds
widest range size (max - min) = 10.3464114832536 microseconds
minimum time = 24.88038277511962 nanoseconds
maximum time = 10.37129186602872 microseconds
50% range = (24.88038277512962 nanoseconds, 24.88038277512962 nanoseconds)
50% range size = 0 nanoseconds