Matching corresponding types between host and device

[jszuppe]

All over the documentation and in the tests we use fundamental C++ types like int, short, long. That may cause problems when their sizes do not match sizes of OpenCL types with the same names.

In particular, I'm talking about long. It's common that on 32-bit OSs sizeof(long) == 4 but for OpenCL long type `sizeof(long) == 8'. Example of code that will fail on 32-bit systems:

boost::compute::vector<long> vec(...);
boost::compute::transform(
  vec.begin(), vec.end(), vec.begin(), boost::compute::identity<long>()
);

Error that we would probably get:

/Users/travis/build/haahh/compute/include/boost/compute/detail/meta_kernel.hpp:451:19: error: no matching function for call to 'type_name'
        stream << type_name<Type>();
                  ^~~~~~~~~~~~~~~
/Users/travis/build/haahh/compute/include/boost/compute/detail/meta_kernel.hpp:375:19: note: in instantiation of function template specialization 'boost::compute::detail::meta_kernel::type<long *>' requested here
        stream << type<T>() << " " << name;
(...)

This is because we do not define type_name<long>() but probably type_name<long long>() as in this case C++ long long is OpenCL long

I think we have to ways to fix that (if you think that needs to be somehow fixed):

• We can put a note/warning about this problem with types in documentation instructing users to use boost::compute::<type_name>_ types (or just to have that issue in mind) and change all types in test to boost::compute::<type_name>_ that have correct size (long --> 'boost::compute::long_` ).
• We can define correct type_name<T>() for every fundamental C++ based on their real size, so if sizeof(long) == 4 then type_name<long>() returns "int" string.