From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/6034 Path: news.gmane.org!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: [RFC] new qsort implementation Date: Mon, 1 Sep 2014 13:17:48 +0200 Message-ID: <20140901111748.GD27258@port70.net> References: <20140901071243.GA6828@duality.lan> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1409570289 20866 80.91.229.3 (1 Sep 2014 11:18:09 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 1 Sep 2014 11:18:09 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-6041-gllmg-musl=m.gmane.org@lists.openwall.com Mon Sep 01 13:18:02 2014 Return-path: Envelope-to: gllmg-musl@plane.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1XOPcX-000761-9s for gllmg-musl@plane.gmane.org; Mon, 01 Sep 2014 13:18:01 +0200 Original-Received: (qmail 9811 invoked by uid 550); 1 Sep 2014 11:18:00 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 9803 invoked from network); 1 Sep 2014 11:18:00 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: <20140901071243.GA6828@duality.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Xref: news.gmane.org gmane.linux.lib.musl.general:6034 Archived-At: * Bobby Bingham [2014-09-01 02:12:43 -0500]: > You can find my test program with this algorithm and others at [4]. > Some of the implementations included are quicksort variants, so the > "qsort-killer" testcase will trigger quadratic behavior in them. If you > want to run this you should consider reducing the maximum input size in > testcases.h, disabling the qsort-killer input at the bottom of > testcases.c, or disabling the affected sort algorithms ("freebsd", > "glibc quicksort", and depending on your libc, "system") in sorters.c. (i had a few build errors: musl_heapsort and musl_smoothsort were not declared in sorters.h and glibc needs -lrt for clock_gettime) smooth sort is best for almost sorted lists when only a few elements are out of order (swap some random elements in a sorted array), this is common in practice so you should test this case too the noise case should use much less noise imho (so you test when only local rearrangements are needed: buffer[i] += random()%small) another common case is sorting two concatenated sorted arrays (merge sort should do better in this case) it would be nice to have a benchmark that is based on common qsort usage cases the qsort-killer test is not very interesting for algorithms other than quicksort (where it is the worst-case), but it would be nice to analyze the worst cases for smoothsort and grailsort (they are both O(n logn) so nothing spectacular is expected but it would be interesting to see how they compare against the theoretical optimum: ceil(lgamma(n)/log(2)) compares) > Here are the numbers comparing musl's current smoothsort with the > attached grailsort code for various input patterns and sizes. The test > was run on x86_64, compiled with gcc 4.8.3 at -Os: > > sorted reverse constant > compares ms compares ms compares ms > musl smoothsort 19976 0 268152 8 19976 0 > 199971 2 3327332 59 199971 2 > 1999963 29 40048748 663 1999963 27 > 19999960 289 465600753 7505 19999960 293 > > grailsort 71024 0 41110 0 28004 0 > 753996 2 412840 5 270727 3 > 7686249 27 4177007 74 2729965 41 > 75927601 277 42751315 901 28243939 436 > interesting that the sorted case is faster with much more compares here on i386 smoothsort is faster sorted reverse constant compares ms compares ms compares ms musl smoothsort 19976 0 268152 7 19976 1 199971 8 3327332 103 199971 15 1999963 105 40048748 1151 1999963 103 19999960 1087 465600753 13339 19999960 1103 grailsort 71024 1 41110 3 28004 3 753996 20 412840 23 270727 23 7686249 151 4177007 370 2729965 224 75927601 1438 42751315 4507 28243939 2353 > #include > #include > > size_t __bsearch(const void *key, const void *base, size_t nel, size_t width, int (*cmp)(const void *, const void *)) > { > size_t baseidx = 0, tryidx; > void *try; > int sign; > > while (nel > 0) { > tryidx = baseidx + nel/2; > try = (char*)base + tryidx*width; > sign = cmp(key, try); > if (!sign) return tryidx; > else if (sign < 0) > nel /= 2; > else { > baseidx = tryidx + 1; > nel -= nel/2 + 1; > } > } > > return ~baseidx; > } > > void *bsearch(const void *key, const void *base, size_t nel, size_t width, int (*cmp)(const void *, const void *)) > { > size_t idx = __bsearch(key, base, nel, width, cmp); > return idx > SSIZE_MAX ? NULL : (char*)base + idx*width; > } musl does not malloc >=SSIZE_MAX memory, but mmap can so baseidx may be >0x7fffffff on a 32bit system i'm not sure if current qsort handles this case