* Simplify the C version of the warp filter to make the intent
  of the code clearer
* Replace saturate_uint() in the C warp filter with an assertion
  that the intermediate values are in-range. This is because they
  should (provably) *never* go out-of-range.
* Add a comment describing the intended hardware architecture
* Miscellaneous comment updates

Change-Id: I798736f923ece599f22d573d31c5dfccd18b2d0e