Date: Thu, 20 Apr 2023 07:50:42 +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: <20CF4C97-7C84-4A4E-984E-E95E406D788C@freebsd.org> In-Reply-To: <1287e42d-3176-1d20-1c84-9bee0243d933@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> <0E123CCD-C06E-443F-8C3C-AFDC8258CCF6@freebsd.org> <1287e42d-3176-1d20-1c84-9bee0243d933@freebsd.org>
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On 20 Apr 2023, at 07:26, Hans Petter Selasky <hselasky@freebsd.org> = wrote: > On 4/20/23 00:31, Jessica Clarke wrote: >> 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. >=20 > Hi, >=20 >> Citation needed. This directly contradicts Rust=E2=80=99s = documentation: >=20 > Sure, look at line 448 in there: >=20 > https://github.com/orlp/pdqsort/blob/master/pdqsort.h#L448 That=E2=80=99s not Rust, and that=E2=80=99s also a comment, not a malloc = call. >>> 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 > Unfortunately it can end up allocating memory. Again. Citation needed. Rust=E2=80=99s documentation says otherwise. Jess >>> 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. >=20 > --HPS
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