Comment the why, not the what

Here's my code: <paste>

Two passes:

1. Delete comments that just restate what the next line does. List
   what you removed.

2. Add comments only where something can't be inferred from the code:
   a non-obvious constraint, why the obvious approach doesn't work
   here, a workaround for an external bug, a magic number's origin,
   an ordering that matters.

If you don't know why something is the way it is, ask me rather than
inventing a reason. A wrong "why" comment is worse than none.