Writing a New Backend

The formal requirements for a backend to class number are given in the reference, but to help speed and simplify the process there is a header skeleton_backend.hpp where all the methods needed to be written are declared but nothing is implemented. The process of writing a new backend then simplifies to:

Save skeleton_backend.hpp under a new name and change its #include guards to match.
Search and replace skeleton_backend to the name of the new backend type.
Fill in the blanks in the class definition and for the compulsary non-members.
Don't forget to mark the functions as inline, constexpr and noexcept as required.
Optionally fill in some of the optional methods - the header declares these in rather verbose form, for example with overloads for every single arithmetic type. No sane backend would ever implement all of these, just choose the ones that make sense and leave the others.
Add convenience typedefs for the actual instantiation(s) of class number that will use the new backend.

To test the new backend, start with a basic arithmetic test, this is a test case under libs/math/test that looks something like:

#include <boost/multiprecision/my_new_number_type.hpp>
#include "test_arithmetic.hpp"

int main()
{
   test<boost::multiprecision::my_new_number_type>();
   return boost::report_errors();
}

This will basically "instantiate everything", and perform a few runtime sanity checks; it is a very good test that you have written legal code!

You should also create a "header include test" that verifies that the new header includes everything it should, see mpfr_include_test.cpp for an example.

For integer types, you should add the new type to at least the following tests as well:

test_hash.cpp
test_int_io.cpp
test_move.cpp
test_numeric_limits.cpp

For floating point types, you should add the new type to at least the following tests as well:

test_acos.cpp
test_asin.cpp
test_atan.cpp
test_constants.cpp
test_cos.cpp
test_cosh.cpp
test_exp.cpp
test_float_io.cpp
test_fpclassify.cpp
test_hash.cpp
test_log.cpp
test_move.cpp
test_numeric_limits.cpp
test_pow.cpp
test_round.cpp
test_sf_import_c99.cpp
test_sin.cpp
test_sinh.cpp
test_sqrt.cpp
test_tan.cpp
test_tanh.cpp
concepts/number_concept_check.cpp
concepts/sf_concept_check_basic.cpp
concepts/sf_concept_check_bessel.cpp
concepts/sf_concept_check_beta.cpp
concepts/sf_concept_check_beta_2.cpp
concepts/sf_concept_check_beta_3.cpp
concepts/sf_concept_check_elliptic.cpp
concepts/sf_concept_check_gamma.cpp
concepts/sf_concept_check_poly.cpp