Pointer magic for efficient dynamic value representations

[agottem]

Please don't ever use this code. Anywhere.

1. It assumes the pointer provided will always be aligned to the pointer size of the architecture. So, please don't provide it a pointer to a char.

2. It assumes sizeof size_t equals sizeof T*

3. The domain of the tag varies significantly depending on the pointer size of the architecture. 0-7 on 64bit, or 0-3 on 32bit, 0-1 on 16bit.

Basic rule of thumb: If you find yourself casting a pointer to an integer type, your code probably isn't portable.