# Objective
Fixes#17983
## Solution
Implemented a basic `Dir4` struct with methods similar to `Dir3` and
`Dir2`.
## Testing
- Did you test these changes? If so, how?
Added unit tests that follow the same pattern of the other Dir structs.
- Are there any parts that need more testing?
Since the other Dir structs use rotations to test renormalization and I
have been following them as a pattern for the Dir4 struct I haven't
implemented a test to cover renormalization of Dir4's.
- How can other people (reviewers) test your changes? Is there anything
specific they need to know?
Use Dir4 in the wild.
- If relevant, what platforms did you test these changes on, and are
there any important ones you can't test?
N/A (Tested on Linux/X11 but it shouldn't be a problem)
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