Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

QVM: Quaternions, Vectors, Matrices

boost/qvm/vec_operations3.hpp

This header defines function and operator overloads that implement all the same operations defined in the boost/qvm/vec_operations.hpp header, but specifically for 2D vectors. You can include it instead of boost/qvm/vec_operations.hpp if you know you don't use vector objects of any other size.