bdiff: write a native version of splitnewlines ./hg perfunidiff mercurial/manifest.py 0 --count 500 --profile before: ! wall 0.309280 comb 0.350000 user 0.290000 sys 0.060000 (best of 32) ./hg perfunidiff mercurial/manifest.py 0 --count 500 --profile after: ! wall 0.241572 comb 0.260000 user 0.240000 sys 0.020000 (best of 39) so it's about 20% faster. I hate Python. I wish we could usefully write this in Rust, but it doesn't look like that's realistic without using the cpython crate, which I'd still like to avoid. Differential Revision: https://phab.mercurial-scm.org/D1973