Fix some style bugs:

Fix some style bugs:
- fix a previous style fix: shifts should be in the correct direction even
  if they are null.
- restore a comment about namespace pollution from floatingpoint.h 1.12 and
  update it.
- remove unused namespace pollution FP_*REG.
- improve some comments.
- sort macro definitions for entry points.
- don't use underscores for macro args.