It’s a 5 step pipeline.

In practice, tree hashing is doing a huge amount of work because most diffs are tiny. Half of all diffs are less than 10 lines, so a hash can extremely quickly match large subtrees.

In a profoundly degenerate case of a C++ header file with only a 20MB array of bytes, it detects a degenerate tree and uses Myers O(N) sequence diffing algorithm instead of treating it as a tree.