In a nutshell, it checks out the target and cherry-picks what had been HEAD onto it, beginning at the merge-base. https://github.com/libgit2/libgit2/blob/maste

In a nutshell, it checks out the target and cherry-picks what had been HEAD onto it, beginning at the merge-base. https://github.com/libgit2/libgit2/blob/master/src/rebase.c https://github.com/libgit2/libgit2/blob/master/src/rebase.c may be helpful and (hopefully) readable.