Re: [boost] [math][distributions] superfluous checking ofparameters?

Subject: Re: [boost] [math][distributions] superfluous checking ofparameters?
From: John Maddock (boost.regex_at_[hidden])
Date: 2011-10-29 12:46:00

>> Why is that? It's done in a consistent way across all distributions. Can 
>> we remove the check
> inside the non
>> member functions that are already checked in the constructor?
>
> As I recollect, I think we thought there were circumstances when this 
> check wasn't redundant (but I
> can't remember the exact case. Users changes the distribution 
> parameters?).
>
> And because it was believed better to be safe than sorry, and the check 
> was very cheap (at runtime),
> we kept it that way.

The issue is like this:

* If the current policy (a template param) is to throw on domain errors (the 
default), then the second check in the non-member functions is redundant as 
any errors will have triggered an exception in the distribution constructor. 
On the other hand:
* If the current policy is to not throw (return NaN on domain errors), then 
the constructor checks are redundant and the non-member function checks are 
the required ones.

If it really is a performance bottleneck, then we could add a check on the 
current exception policy so that those two mutually exclusive options get 
optimized at compile time.

HTH, John.