Auto-formatting a source file in emacs

Question

How do I apply a set of formatting rules to an existing source file in emacs?

Specifically I have an assembly (*.s) file, but I would like a generic command

Answer 1

if you want indent current buffer

(defun iwb ()
  "indent whole buffer"
  (interactive)
  (delete-trailing-whitespace)
  (indent-region (point-min) (point-max) nil)
  (untabify (point-min) (point-max)))