[Boost-users] Multiprecison: converting a complex class to a number<> backend

Subject: [Boost-users] Multiprecison: converting a complex class to a number<> backend
From: Daniel Brake (danielthebrake_at_[hidden])
Date: 2016-06-28 15:49:52

Hi Boost,

I have implemented my own complex class wrapping around
Boost.Multiprecision number<>, particularly mpfr_float.  Now, I'd like to
take the class I've written, and extend/convert it into a backend suitable
for use in number<>.  While I've read the documentation describing the
requirements for a backend
<http://www.boost.org/doc/libs/1_61_0/libs/multiprecision/doc/html/boost_multiprecision/ref/backendconc.html>,
and think I understand what I need to do, I have found 0 examples in the
wild.

My current setup has a pair of files mpfr_complex.hpp, mpfr_complex.cpp
describing something like (just what you'd expect, really)

---------
class complex{
    mpfr_float real_, imag_;

    public:
    // the *= family of operators, getters, setters,
    // some factory functions, etc
};

//the free operators defined down here, along with pow, exp, etc.
--------------

I think what I'd like to write is a new complex_backend.hpp file which
implements the required functions for the complex wrapper around
mpfr_float.  In this file, I believe I implement the family of functions
such as
eval_multiply(b, a)
in terms of the operators for my complex class.  Is this right?

In a related vein, with et_on for mpfr_float, I've started adding templated
overloads for the complex operators and math function accepting expressions
of reals, and I think this is going to get out of hand, so using number<>
would conceivably save me a ton of time writing my own functions.  It will
also save me a ton of errors for hand-writing the expression templates for
complexes, which appear to be ready to go from Boost.Multiprecision once I
get a backend implemented.

Again, my goal is expression templates for complexes with real and
imaginary fields consisting of mpfr_floats, leveraging the number<>
template, with et_on, and my own backend.  Do you have any advice?  Any
references to any other custom backends?

Daniel Brake
University of Notre Dame
Applied and Computational Mathematics and Statistics