Date: Wed, 19 Apr 2023 23:31:19 +0100 From: Jessica Clarke <jrtc27@freebsd.org> To: Hans Petter Selasky <hselasky@freebsd.org> Cc: Brooks Davis <brooks@freebsd.org>, src-committers <src-committers@freebsd.org>, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 8dcf3a82c54c - main - libc: Implement bsort(3) a bitonic type of sorting algorithm. Message-ID: <0E123CCD-C06E-443F-8C3C-AFDC8258CCF6@freebsd.org> In-Reply-To: <42d63675-9b1f-70dc-a1da-fef3d43790fd@freebsd.org> References: <202304191206.33JC6Qcp062380@gitrepo.freebsd.org> <ZEAM3rO9r5e97BHE@spindle.one-eyed-alien.net> <a073fd36-9aa9-e988-0cc5-86af305fb654@freebsd.org> <3B5734C4-8630-4CD5-BA8D-DE33899161F1@freebsd.org> <e2ea5c89-aa48-e257-b9d5-7fe783bf216e@freebsd.org> <2840BE79-CC25-427A-A5E9-476A38E749E3@freebsd.org> <42d63675-9b1f-70dc-a1da-fef3d43790fd@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 19 Apr 2023, at 22:41, Hans Petter Selasky <hselasky@freebsd.org> = wrote: >=20 > On 4/19/23 22:17, Jessica Clarke wrote: >> pdqsort is n log n time, in-place and doesn=E2=80=99t allocate, and = is used, >> for example, for Rust=E2=80=99s standard sort_unstable. >=20 > Hi Jessica, >=20 > Like many many people have tried over the years, to improve the = belated QuickSort (*) algorithm since it was invented, by catching bad = behaviour and then fallback to other algorithms, pdqsort() is not a = solution! >=20 > Yes, it is probably "N log N" time, but if you read the code = carefully, it falls back to heapsort(), which indeed uses malloc(), = which is exactly my point, that I want to avoid. Citation needed. This directly contradicts Rust=E2=80=99s documentation: > This sort is unstable (i.e., may reorder equal elements), in-place = (i.e., does not allocate), and O(n * log(n)) worst-case. >=20 > Current implementation > The current algorithm is based on pattern-defeating quicksort by Orson = Peters, which combines the fast average case of randomized quicksort = with the fast worst case of heapsort, while achieving linear time on = slices with certain patterns. It uses some randomization to avoid = degenerate cases, but with a fixed seed to always provide deterministic = behavior. -- = https://doc.rust-lang.org/std/primitive.slice.html#method.sort_unstable > Please come forward with a "N log N" time algorithm which is malloc() = and alloca() free, and then we'll talk! >=20 > And not at least BSD-2-clause licensed and not covered by any patents, = GPLv2 or whatever! Rust=E2=80=99s meets that and is MIT or Apache 2.0. The original = pdqsort=E2=80=99s also does and is under the zlib license. I=E2=80=99m not including alloca() = free, because that=E2=80=99s a nonsense restriction that would forbid any = local variables. Jess
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?0E123CCD-C06E-443F-8C3C-AFDC8258CCF6>