Reformat code in little-endian patch

[snicolet]

Reformat code and rename the function to "read_little_endian()" in the recent
commit by Ronald de Man for support of big endian systems.

closes #3016

No functional change

[syzygy1]

The cast relies on implementation-defined behaviour, which is why I used memcpy(). Of course any sane compiler implementation will leave the underlying bits unaffected...

[vondele]

yes, I agree that the use of memcpy here is the recommended way of doing this. I think our CI might pick this up.

[syzygy1]

Looks like C++20 will allow us to get rid of the memcpy():
https://stackoverflow.com/questions/13150449/efficient-unsigned-to-signed-cast-avoiding-implementation-defined-behavior

[snicolet]

Fine with me (except if there is a retinterpret_blah_blah_cast() in the C++ standard for doing that, of course)..

[syzygy1]

No, reinterpret_cast can't be used for this, I tried :-). Apparently that is meant for pointers.

[syzygy1]

Well, perhaps one could reinterpret_cast a pointer to the unsigned value as a pointer to a signed value and then read it out...

[vondele]

I think memcpy is just fine for now. The compiler will replace the call, there is no performance impact, and right now this is a relatively clean way to do things.

[snicolet]

I will squash the two commits into one.

Done, patch is ready IMO.

[gvreuls]

Well, perhaps one could reinterpret_cast a pointer to the unsigned value as a pointer to a signed value and then read it out...

That's implementation dependent behavior too. In C++ (as opposed to C) you can only read memory that has been initialized by a constructor for the correct type and the only way around this is std::memcpy. This also means that the use of unions for casting is implementation dependent in C++ (but not in C), which makes the Score <-> Value functions make_score (uses a cast) and both mg_value and eg_value (use unions) not perfectly portable C++ (they don't cause any problems on architectures and compilers we support though).

[syzygy1]

@gvreuls mg_value() and eg_value() have been the subject of debate :-) See #211 and #849.

[snicolet]

Merged via 81d716f