[eigen] Re: Rework of numtraits / math functions (note: all integer types are now supported!)

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2010/4/28 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
> Hi List,
>
> *** The big news ***
>
> All integer types, from "unsigned char" to "long long", are now
> correctly supported. There's a new unit test for that: integer_types.
>
> This is a consequence of a big rework of NumTraits (does no longer
> inherit numeric_limits) and of our global math functions (ei_sin...)
> which are now templated.
>
> *** Interface changes ***
>
> All that also means some interface changes if you are adding support
> for custom types.
>
> The NumTraits changes are small, see the "Customizing Eigen" dox page
> once it'll be updated.
>
> For the math functions, the changes are a bit bigger as you can see in
> MathFunctions.h. Let's take ei_sin as an example. It's a matter of
> adding a specialization of a struct ei_sin_impl<Scalar> for your type.
> Suppose that you want to add ei_sin() support for your custom
> FixedPoint type. You'd do something like that:
>
> namespace Eigen
> {

template<>
>  struct ei_sin_impl<FixedPoint>
>  {
>    // here you tell Eigen what's the return type of ei_sin(FixedPoint)
>    typedef FixedPoint retval;

Ooh, thinking more about it, you really shouldn't have to specify it
since Eigen knows it already. I'll change that so it's not needed.

Benoit

>
>    // and here you implement the function
>    static inline FixedPoint run(const FixedPoint& x)
>    {
>      return my_fixedpoint_sin_function(x);
>    }
>  };
> }
>
> So yes, that's more verbose than before. But isn't it worth it, to get
> that generic system that supports e.g. all integer types for free?
> Another remark is that part of our global math functions were already
> like that (e.g. ei_random) so we used to have a discrepancy between
> templated and non-templated functions. Finally, if a user has to
> support a lot of math functions for his custom type, he'll be able to
> write a macro to factor the code.
>
> *** Call for good wills ***
>
> If you're looking for a useful task to accomplish, here's one: update
> the dox page (doc/I00_CustomizingEigen.dox) to explain how to do these
> specializations of math functions (like above). Instead of Adolc's
> adouble which is quite special, and already handled in an unsupported
> module, how about carrying on the FixedPoint example?
>
> *** Testing needed ***
>
> Especially in the Array support (so 'array' unit test), I'm using
> SFINAE, that is highly susceptible of breaking MSC support.
>
> Benoit
>