On Mon, 28 Jul 2025, Junio C Hamano wrote: > Alexander Monakov <amonakov@xxxxxxxxx> writes: > > > I've noticed the work by Phillip Wood regarding hash optimization for xdiff. > > I want to point out that it is possible to speed up the existing hash by 1.5x > > matching the peformance of xxhash (but without introducing a dependendency). > > Using xxhash() was merely a sample code path for technology > demonstration, so the Rust adoption topic may want to pick a > different code path to do its thing. My interest here is just speeding up xdiff in C, is that a welcome topic? > > The additive variant of the djb2 hash is used in ELF symbol lookup, and > > Noah Goldstein contributed a well-optimized implementation to Glibc. > > What is the licensing terms for that code you are proposing us to > borrow? If it is anything recent in GNU, I'd expect that it would > be GPLv3, which would be incompatible with our code base? Noah's code is not usable in xdiff due to different context (mainly the need to limit iteration by length — ELF hashing iterates until the NUL character). I have participated in review of Noah's patches and he kindly listed me as a co-author in the final revision of his patchset. So while I'm aware of how his code is structured, I had to write a new implementation in order to meet the contract of xdl_hash_record_verbatim. Therefore I think I can contribute this code on GPLv2 terms with my sign-off. Maybe someone would be willing to look at patch 2 and compare against Noah's patch (linked in the commit message)? Thank you. Alexander
