Date: Thu, 20 Apr 2023 09:08:42 +0200 From: Hans Petter Selasky <hselasky@freebsd.org> To: Jessica Clarke <jrtc27@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: <2012a30a-ac2c-46cc-eb25-ea8970e6d170@freebsd.org> In-Reply-To: <20CF4C97-7C84-4A4E-984E-E95E406D788C@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> <20CF4C97-7C84-4A4E-984E-E95E406D788C@freebsd.org>
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On 4/20/23 08:50, Jessica Clarke wrote: > 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: >>>> >>>> On 4/19/23 22:17, Jessica Clarke wrote: >>>>> pdqsort is n log n time, in-place and doesn’t allocate, and is used, >>>>> for example, for Rust’s standard sort_unstable. >>>> >>>> Hi Jessica, >>>> >>>> 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! >>>> >>>> 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. >> >> Hi, >> >>> Citation needed. This directly contradicts Rust’s documentation: >> >> Sure, look at line 448 in there: >> >> https://github.com/orlp/pdqsort/blob/master/pdqsort.h#L448 > > That’s not Rust, and that’s 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. >> >> Unfortunately it can end up allocating memory. > > Again. Citation needed. Rust’s documentation says otherwise. Hi Jessica, Here are my citations: cd /usr/ports/lang/rust make extract less work/rustc-1.68.2-src/library/alloc/src/slice.rs /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] 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. less /usr/src/lib/libc/stdlib/heapsort.c The first thing heapsort() does is go and grab memory: > if ((k = malloc(size)) == NULL) > return (-1); --HPS
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