Re: [Toon-members] Precision in SE3::exp()

[Simon Taylor]

 > ok, so the problem is with the patch or without ?

For me, the patch "fixes" the difference in behaviour - that is, gives 
the same output both with and without a "using namespace std;".

> it should probably be done similar to sqrt:
>
> using std::cos, std::sin;
>
> and later sin(Precision p)
>
> This is useful, if Precision is something completely different, for example 
> automatic differentiation class (like FADBAD++ that I am using). then the 
> compiler will also look in the namespaces of the Precision type to find a 
> matching sin overload. Otherwise, if there isn't one in std:: it will fail.

That makes sense. I always forget about C++ doing that search for 
functions in the namespace of the parameters, that's pretty neat.

> but, I tried to test this with FADBAD++ and it didn't fail :/

Hmm, can the types be implicitly converted to double or something?

> In anycase shouldn't there be a warning, then the double expression is assigned 
> to the float value at the end ? this should provide some heads-up that there is 
> something going on.

That warning isn't enabled by default on GCC, it's not in -Wall or 
-Wextra, and needs to be specifically requested with -Wconversion. I 
hadn't realised that until today, but it's now part of my standard 
warning flags.

The other interesting warning flag is -Wdouble-promotion, which warns 
when some floats are promoted to double for an expression:
float f=1.3f;
if(f < 2.4) // f promoted to double here for the comparison

Obviously the promotion above won't change behaviour, but it might be 
undesirable on platforms without hardware floating point. I guess for 
float/double that could be fixed to if(f < Precision(2.4)) - would that 
have any problems generalising to FADBAD++ or other types? Also, it's 
pretty ugly, so might not be something we want to sprinkle liberally 
throughout TooN.

Simon

> cheers,
>    Gerhard
>
> > I've been trying to find a list of C++ overloads that are added std to search for all 
> > potential occurrences of these sorts of issues but I haven't had much luck. There's a 
> > couple of gcc options that help tracking them down in code that actually gets compiled 
> > (-Wdouble-promotion and -Wconversion) but I don't think there's a warning for implicit 
> > parameter conversion (I can't make "double v = ::sqrt(1.3f);" generate any 
> > warnings, but having v as a float makes -Wconversion pick it up as possible data loss).
> >
> > Simon
> >
> > ps: since the git switch we seem to have lost commit email notifications...
> > <explicit_std_namespace.patch>_______________________________________________
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>
> --
> Submit to ISMAR 2012 - http://ismar.vgtc.org/
>
> Gerhard Reitmayr
> Institute for Computer Graphics and Vision
> http://www.icg.tugraz.at/Members/gerhard
> tel: ++43 316 873 5082