I believe git uses its own implementation for applying deltas sucked down by `git pull` https://github.com/git/git/blob/master/patch-delta.c There's also

I believe git uses its own implementation for applying deltas sucked down by `git pull` https://github.com/git/git/blob/master/patch-delta.c There's also `git apply` that applies user supplied patchfiles but if I'm reading this correctly it also uses an internal implementation: https://github.com/git/git/blob/master/apply.c