Re: [Boost-users] [TR1 Review] TR1 Formal Review Beginning

From: John Maddock (john_at_[hidden])
Date: 2005-09-30 11:18:45

> At the risk of being irritating, I'm going to ask just the opposite
> question. ;-)
>
> Why is hypot (for example) templated?

Good question, I needed hypot to implement some of the complex number stuff, 
and it's a template because it was possible to make it one :-)

> template <class T>
> T hypot(T x, T y);
>
> If the intent is to implement 8.16.4 (from N1836), I don't think this
> does it.  Consider this test for example:

I'm aware of those nasties, but <cmath> is *not* part of the current 
submission, well that's my excuse anyway.  Basically hypot/log1p/expm1 are 
some internals I needed and it seems a shame not to expose them in 
Boost.Math.

I have jumped though hoops however to make sure that <complex> does the 
right thing with for example:

polar(2.3, char(1));  // expression returns a std::complex<double>

> Also do we want to support infinities and nans?
>
> assert(hypot(INFINITY, sqrt(-1.)) == INFINITY);

Hmm, what does C99 say about this, I can see anything obvious at first 
glance?  Your suggestion matches what the complex number functions are 
required to do however, so it's probably in there somewhere, I just can't 
see it at present.  I'm not sure I handle range errors correctly either 
(setting errno that is).

It would certainly be easy enough to convert those functions into 
non-template inlines that forward to the template implementation, and make 
them C99 conforming in the process (once I've figured out what that is!)

Thanks for raising this,

John.