Review Board uses a version of the Meyers Diff algorithm for the diff viewer,

which is pretty standard and widely-used. However, unclear diff might be

reported under some scenarios. For example, when user switched order of a big

chunk of code with each other, meyer diff will see it as a change line by line

instead of being aware that the whole block is switched. Patience differ

tackles issues like these by scanning the whole file and actively seeking out

interesting lines before applying diff while sacrificing some performances.
This is a backend feature and it has not been updated to be the default method

of diffing. To test this feature, you could go to

reviewboard/diffviewer/differ.py, and update line 26 to DEFAULT = PATIENCE.

Unit tests are created in reviewboard/diffviewer/tests/test_patiencediff.py.

You can run the test by

./tests/runtests.py reviewboard.diffviewer.tests.test_patiencediff:PatienceDifferTest.

All unit tests have passed.