From: Jarkko Hietaniemi Date: Wed, 30 Aug 2000 22:14:13 +0000 (+0000) Subject: Change the internal implementation of sort() to be mergesort X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=be7ddd5d2d1ac50e54898aa4f400140ded3a1297;p=p5sagit%2Fp5-mst-13.2.git Change the internal implementation of sort() to be mergesort instead of quicksort, from John Linderman . Gives us better worst case, better average case, and stability. What's there not to like? (Small fixes for threaded builds were required). p4raw-id: //depot/perl@6927 --- diff --git a/pod/perldelta.pod b/pod/perldelta.pod index 4e6ecea..70d2113 100644 --- a/pod/perldelta.pod +++ b/pod/perldelta.pod @@ -286,6 +286,17 @@ distribution. map() that changes the size of the list should now work faster. +=sort * + +sort() has been changed to use mergesort internally as opposed to the +earlier quicksort. For very small lists this may result in slightly +slower sorting times, but in general the speedup should be at least 20%. +Additional bonuses are that the worst case behaviour of sort() is now +better (in computer science terms it is now O(N log N), as opposed to +O(N**2) of quicksort), and that sort() is now stable (meaning that +elements with identical keys will stay ordered as they were before +the sort). + =back =head1 Installation and Configuration Improvements diff --git a/pp_ctl.c b/pp_ctl.c index 45f9a7e..01b8fec 100644 --- a/pp_ctl.c +++ b/pp_ctl.c @@ -3672,683 +3672,383 @@ S_doparseform(pTHX_ SV *sv) SvCOMPILED_on(sv); } -/* - * The rest of this file was derived from source code contributed - * by Tom Horsley. - * - * NOTE: this code was derived from Tom Horsley's qsort replacement - * and should not be confused with the original code. - */ - -/* Copyright (C) Tom Horsley, 1997. All rights reserved. - - Permission granted to distribute under the same terms as perl which are - (briefly): - - This program is free software; you can redistribute it and/or modify - it under the terms of either: - a) the GNU General Public License as published by the Free - Software Foundation; either version 1, or (at your option) any - later version, or +#ifdef TESTHARNESS +#include +typedef void SV; +#define pTHXo_ +#define pTHX_ +#define STATIC +#define New(ID,VAR,N,TYPE) VAR=(TYPE *)malloc((N)*sizeof(TYPE)) +#define Safefree(VAR) free(VAR) +typedef int (*SVCOMPARE_t) (pTHXo_ SV*, SV*); +#endif /* TESTHARNESS */ + +typedef char * aptr; /* pointer for arithmetic on sizes */ +typedef SV * gptr; /* pointers in our lists */ + +/* Copyright notice from Peter's original sort, +** which has been modified heavily. Good ideas are Peter's +** bugs are jpl's +*/ - b) the "Artistic License" which comes with this Kit. +/* Much of this code is original source code from BSD4.4, and is + * copyright (c) 1991 The Regents of the University of California. + * + * 1. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 2. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 3. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * +*/ - Details on the perl license can be found in the perl source code which - may be located via the www.perl.com web page. +/* + * AUTHOR: Peter McIlroy + * 1991-1992, See: Optimistic Merge Sort (SODA '92) +*/ - This is the most wonderfulest possible qsort I can come up with (and - still be mostly portable) My (limited) tests indicate it consistently - does about 20% fewer calls to compare than does the qsort in the Visual - C++ library, other vendors may vary. +/* Binary merge internal sort, with a few special mods +** for the special perl environment it now finds itself in. +** +** Things that were once options have been hotwired +** to values suitable for this use. In particular, we'll always +** initialize looking for natural runs, we'll always produce stable +** output, and we'll always do Peter McIlroy's binary merge. +*/ - Some of the ideas in here can be found in "Algorithms" by Sedgewick, - others I invented myself (or more likely re-invented since they seemed - pretty obvious once I watched the algorithm operate for a while). +/* Pointer types for arithmetic and storage and convenience casts */ - Most of this code was written while watching the Marlins sweep the Giants - in the 1997 National League Playoffs - no Braves fans allowed to use this - code (just kidding :-). +#define APTR(P) ((aptr)(P)) +#define GPTP(P) ((gptr *)(P)) +#define GPPP(P) ((gptr **)(P)) - I realize that if I wanted to be true to the perl tradition, the only - comment in this file would be something like: - ...they shuffled back towards the rear of the line. 'No, not at the - rear!' the slave-driver shouted. 'Three files up. And stay there... +/* byte offset from pointer P to (larger) pointer Q */ +#define BYTEOFF(P, Q) (APTR(Q) - APTR(P)) - However, I really needed to violate that tradition just so I could keep - track of what happens myself, not to mention some poor fool trying to - understand this years from now :-). -*/ +#define PSIZE sizeof(gptr) -/* ********************************************************** Configuration */ +/* If PSIZE is power of 2, make PSHIFT that power, if that helps */ -#ifndef QSORT_ORDER_GUESS -#define QSORT_ORDER_GUESS 2 /* Select doubling version of the netBSD trick */ +#ifdef PSHIFT +#define PNELEM(P, Q) (BYTEOFF(P,Q) >> (PSHIFT)) +#define PNBYTE(N) ((N) << (PSHIFT)) +#define PINDEX(P, N) (GPTP(APTR(P) + PNBYTE(N))) +#else +/* Leave optimization to compiler */ +#define PNELEM(P, Q) (GPTP(Q) - GPTP(P)) +#define PNBYTE(N) ((N) * (PSIZE)) +#define PINDEX(P, N) (GPTP(P) + (N)) #endif -/* QSORT_MAX_STACK is the largest number of partitions that can be stacked up for - future processing - a good max upper bound is log base 2 of memory size - (32 on 32 bit machines, 64 on 64 bit machines, etc). In reality can - safely be smaller than that since the program is taking up some space and - most operating systems only let you grab some subset of contiguous - memory (not to mention that you are normally sorting data larger than - 1 byte element size :-). -*/ -#ifndef QSORT_MAX_STACK -#define QSORT_MAX_STACK 32 -#endif +/* Pointer into other corresponding to pointer into this */ +#define POTHER(P, THIS, OTHER) GPTP(APTR(OTHER) + BYTEOFF(THIS,P)) -/* QSORT_BREAK_EVEN is the size of the largest partition we should insertion sort. - Anything bigger and we use qsort. If you make this too small, the qsort - will probably break (or become less efficient), because it doesn't expect - the middle element of a partition to be the same as the right or left - - you have been warned). -*/ -#ifndef QSORT_BREAK_EVEN -#define QSORT_BREAK_EVEN 6 -#endif +#define FROMTOUPTO(src, dst, lim) do *dst++ = *src++; while(src 0 as the value of elt1 is < elt2, == elt2, > elt2 -*/ -#define qsort_cmp(elt1, elt2) \ - ((*compare)(aTHXo_ array[elt1], array[elt2])) +#define PTHRESH (8) -#ifdef QSORT_ORDER_GUESS -#define QSORT_NOTICE_SWAP swapped++; -#else -#define QSORT_NOTICE_SWAP -#endif - -/* swaps contents of array elements elt1, elt2. -*/ -#define qsort_swap(elt1, elt2) \ - STMT_START { \ - QSORT_NOTICE_SWAP \ - temp = array[elt1]; \ - array[elt1] = array[elt2]; \ - array[elt2] = temp; \ - } STMT_END - -/* rotate contents of elt1, elt2, elt3 such that elt1 gets elt2, elt2 gets - elt3 and elt3 gets elt1. +/* RTHRESH is the number of elements in a run that must compare low +** to the low element from the opposing run before we justify +** doing a binary rampup instead of single stepping. +** In random input, N in a row low should only happen with +** probability 2^(1-N), so we can risk that we are dealing +** with orderly input without paying much when we aren't. */ -#define qsort_rotate(elt1, elt2, elt3) \ - STMT_START { \ - QSORT_NOTICE_SWAP \ - temp = array[elt1]; \ - array[elt1] = array[elt2]; \ - array[elt2] = array[elt3]; \ - array[elt3] = temp; \ - } STMT_END -/* ************************************************************ Debug stuff */ +#define RTHRESH (6) -#ifdef QSORT_DEBUG -static void -break_here() -{ - return; /* good place to set a breakpoint */ -} +/* +** Overview of algorithm and variables. +** The array of elements at list1 will be organized into runs of length 2, +** or runs of length >= 2 * PTHRESH. We only try to form long runs when +** PTHRESH adjacent pairs compare in the same way, suggesting overall order. +** +** Unless otherwise specified, pair pointers address the first of two elements. +** +** b and b+1 are a pair that compare with sense ``sense''. +** b is the ``bottom'' of adjacent pairs that might form a longer run. +** +** p2 parallels b in the list2 array, where runs are defined by +** a pointer chain. +** +** t represents the ``top'' of the adjacent pairs that might extend +** the run beginning at b. Usually, t addresses a pair +** that compares with opposite sense from (b,b+1). +** However, it may also address a singleton element at the end of list1, +** or it may be equal to ``last'', the first element beyond list1. +** +** r addresses the Nth pair following b. If this would be beyond t, +** we back it off to t. Only when r is less than t do we consider the +** run long enough to consider checking. +** +** q addresses a pair such that the pairs at b through q already form a run. +** Often, q will equal b, indicating we only are sure of the pair itself. +** However, a search on the previous cycle may have revealed a longer run, +** so q may be greater than b. +** +** p is used to work back from a candidate r, trying to reach q, +** which would mean b through r would be a run. If we discover such a run, +** we start q at r and try to push it further towards t. +** If b through r is NOT a run, we detect the wrong order at (p-1,p). +** In any event, after the check (if any), we have two main cases. +** +** 1) Short run. b <= q < p <= r <= t. +** b through q is a run (perhaps trivial) +** q through p are uninteresting pairs +** p through r is a run +** +** 2) Long run. b < r <= q < t. +** b through q is a run (of length >= 2 * PTHRESH) +** +** Note that degenerate cases are not only possible, but likely. +** For example, if the pair following b compares with opposite sense, +** then b == q < p == r == t. +*/ -#define qsort_assert(t) (void)( (t) || (break_here(), 0) ) static void -doqsort_all_asserts( - void * array, - size_t num_elts, - size_t elt_size, - int (*compare)(const void * elt1, const void * elt2), - int pc_left, int pc_right, int u_left, int u_right) +dynprep(pTHX_ gptr *list1, gptr *list2, size_t nmemb, SVCOMPARE_t cmp) { - int i; - - qsort_assert(pc_left <= pc_right); - qsort_assert(u_right < pc_left); - qsort_assert(pc_right < u_left); - for (i = u_right + 1; i < pc_left; ++i) { - qsort_assert(qsort_cmp(i, pc_left) < 0); - } - for (i = pc_left; i < pc_right; ++i) { - qsort_assert(qsort_cmp(i, pc_right) == 0); - } - for (i = pc_right + 1; i < u_left; ++i) { - qsort_assert(qsort_cmp(pc_right, i) < 0); - } + int sense; + register gptr *b, *p, *q, *t, *p2; + register gptr c, *last, *r; + gptr *savep; + + b = list1; + last = PINDEX(b, nmemb); + sense = (cmp(aTHX_ *b, *(b+1)) > 0); + for (p2 = list2; b < last; ) { + /* We just started, or just reversed sense. + ** Set t at end of pairs with the prevailing sense. + */ + for (p = b+2, t = p; ++p < last; t = ++p) { + if ((cmp(aTHX_ *t, *p) > 0) != sense) break; + } + q = b; + /* Having laid out the playing field, look for long runs */ + do { + p = r = b + (2 * PTHRESH); + if (r >= t) p = r = t; /* too short to care about */ + else { + while (((cmp(aTHX_ *(p-1), *p) > 0) == sense) && + ((p -= 2) > q)); + if (p <= q) { + /* b through r is a (long) run. + ** Extend it as far as possible. + */ + p = q = r; + while (((p += 2) < t) && + ((cmp(aTHX_ *(p-1), *p) > 0) == sense)) q = p; + r = p = q + 2; /* no simple pairs, no after-run */ + } + } + if (q > b) { /* run of greater than 2 at b */ + savep = p; + p = q += 2; + /* pick up singleton, if possible */ + if ((p == t) && + ((t + 1) == last) && + ((cmp(aTHX_ *(p-1), *p) > 0) == sense)) + savep = r = p = q = last; + p2 = NEXT(p2) = p2 + (p - b); + if (sense) while (b < --p) { + c = *b; + *b++ = *p; + *p = c; + } + p = savep; + } + while (q < p) { /* simple pairs */ + p2 = NEXT(p2) = p2 + 2; + if (sense) { + c = *q++; + *(q-1) = *q; + *q++ = c; + } else q += 2; + } + if (((b = p) == t) && ((t+1) == last)) { + NEXT(p2) = p2 + 1; + b++; + } + q = r; + } while (b < t); + sense = !sense; + } + return; } -#define qsort_all_asserts(PC_LEFT, PC_RIGHT, U_LEFT, U_RIGHT) \ - doqsort_all_asserts(array, num_elts, elt_size, compare, \ - PC_LEFT, PC_RIGHT, U_LEFT, U_RIGHT) - -#else -#define qsort_assert(t) ((void)0) +/* Overview of bmerge variables: +** +** list1 and list2 address the main and auxiliary arrays. +** They swap identities after each merge pass. +** Base points to the original list1, so we can tell if +** the pointers ended up where they belonged (or must be copied). +** +** When we are merging two lists, f1 and f2 are the next elements +** on the respective lists. l1 and l2 mark the end of the lists. +** tp2 is the current location in the merged list. +** +** p1 records where f1 started. +** After the merge, a new descriptor is built there. +** +** p2 is a ``parallel'' pointer in (what starts as) descriptor space. +** It is used to identify and delimit the runs. +** +** In the heat of determining where q, the greater of the f1/f2 elements, +** belongs in the other list, b, t and p, represent bottom, top and probe +** locations, respectively, in the other list. +** They make convenient temporary pointers in other places. +*/ -#define qsort_all_asserts(PC_LEFT, PC_RIGHT, U_LEFT, U_RIGHT) ((void)0) +STATIC void +S_qsortsv(pTHX_ gptr *list1, size_t nmemb, SVCOMPARE_t cmp) +{ + int i, run; + int sense; + register gptr *f1, *f2, *t, *b, *p, *tp2, *l1, *l2, *q; + gptr *aux, *list2, *p2, *last; + gptr *base = list1; + gptr *p1; + + if (nmemb <= 1) return; /* sorted trivially */ + New(799,list2,nmemb,gptr); /* allocate auxilliary array */ + aux = list2; + dynprep(aTHX_ list1, list2, nmemb, cmp); + last = PINDEX(list2, nmemb); + while (NEXT(list2) != last) { + /* More than one run remains. Do some merging to reduce runs. */ + l2 = p1 = list1; + for (tp2 = p2 = list2; p2 != last;) { + /* The new first run begins where the old second list ended. + ** Use the p2 ``parallel'' pointer to identify the end of the run. + */ + f1 = l2; + t = NEXT(p2); + f2 = l1 = POTHER(t, list2, list1); + if (t != last) t = NEXT(t); + l2 = POTHER(t, list2, list1); + p2 = t; + while (f1 < l1 && f2 < l2) { + /* If head 1 is larger than head 2, find ALL the elements + ** in list 2 strictly less than head1, write them all, + ** then head 1. Then compare the new heads, and repeat, + ** until one or both lists are exhausted. + ** + ** In all comparisons (after establishing + ** which head to merge) the item to merge + ** (at pointer q) is the first operand of + ** the comparison. When we want to know + ** if ``q is strictly less than the other'', + ** we can't just do + ** cmp(q, other) < 0 + ** because stability demands that we treat equality + ** as high when q comes from l2, and as low when + ** q was from l1. So we ask the question by doing + ** cmp(q, other) <= sense + ** and make sense == 0 when equality should look low, + ** and -1 when equality should look high. + */ + + + if (cmp(aTHX_ *f1, *f2) <= 0) { + q = f2; b = f1; t = l1; + sense = -1; + } else { + q = f1; b = f2; t = l2; + sense = 0; + } -#endif -/* ****************************************************************** qsort */ + /* ramp up + ** + ** Leave t at something strictly + ** greater than q (or at the end of the list), + ** and b at something strictly less than q. + */ + for (i = 1, run = 0 ;;) { + if ((p = PINDEX(b, i)) >= t) { + /* off the end */ + if (((p = PINDEX(t, -1)) > b) && + (cmp(aTHX_ *q, *p) <= sense)) + t = p; + else b = p; + break; + } else if (cmp(aTHX_ *q, *p) <= sense) { + t = p; + break; + } else b = p; + if (++run >= RTHRESH) i += i; + } -STATIC void -S_qsortsv(pTHX_ SV ** array, size_t num_elts, SVCOMPARE_t compare) -{ - register SV * temp; - struct partition_stack_entry partition_stack[QSORT_MAX_STACK]; - int next_stack_entry = 0; + /* q is known to follow b and must be inserted before t. + ** Increment b, so the range of possibilities is [b,t). + ** Round binary split down, to favor early appearance. + ** Adjust b and t until q belongs just before t. + */ - int part_left; - int part_right; -#ifdef QSORT_ORDER_GUESS - int qsort_break_even; - int swapped; -#endif + b++; + while (b < t) { + p = PINDEX(b, (PNELEM(b, t) - 1) / 2); + if (cmp(aTHX_ *q, *p) <= sense) { + t = p; + } else b = p + 1; + } - /* Make sure we actually have work to do. - */ - if (num_elts <= 1) { - return; - } - - /* Setup the initial partition definition and fall into the sorting loop - */ - part_left = 0; - part_right = (int)(num_elts - 1); -#ifdef QSORT_ORDER_GUESS - qsort_break_even = QSORT_BREAK_EVEN; -#else -#define qsort_break_even QSORT_BREAK_EVEN -#endif - for ( ; ; ) { - if ((part_right - part_left) >= qsort_break_even) { - /* OK, this is gonna get hairy, so lets try to document all the - concepts and abbreviations and variables and what they keep - track of: - - pc: pivot chunk - the set of array elements we accumulate in the - middle of the partition, all equal in value to the original - pivot element selected. The pc is defined by: - - pc_left - the leftmost array index of the pc - pc_right - the rightmost array index of the pc - - we start with pc_left == pc_right and only one element - in the pivot chunk (but it can grow during the scan). - - u: uncompared elements - the set of elements in the partition - we have not yet compared to the pivot value. There are two - uncompared sets during the scan - one to the left of the pc - and one to the right. - - u_right - the rightmost index of the left side's uncompared set - u_left - the leftmost index of the right side's uncompared set - - The leftmost index of the left sides's uncompared set - doesn't need its own variable because it is always defined - by the leftmost edge of the whole partition (part_left). The - same goes for the rightmost edge of the right partition - (part_right). - - We know there are no uncompared elements on the left once we - get u_right < part_left and no uncompared elements on the - right once u_left > part_right. When both these conditions - are met, we have completed the scan of the partition. - - Any elements which are between the pivot chunk and the - uncompared elements should be less than the pivot value on - the left side and greater than the pivot value on the right - side (in fact, the goal of the whole algorithm is to arrange - for that to be true and make the groups of less-than and - greater-then elements into new partitions to sort again). - - As you marvel at the complexity of the code and wonder why it - has to be so confusing. Consider some of the things this level - of confusion brings: - - Once I do a compare, I squeeze every ounce of juice out of it. I - never do compare calls I don't have to do, and I certainly never - do redundant calls. - - I also never swap any elements unless I can prove there is a - good reason. Many sort algorithms will swap a known value with - an uncompared value just to get things in the right place (or - avoid complexity :-), but that uncompared value, once it gets - compared, may then have to be swapped again. A lot of the - complexity of this code is due to the fact that it never swaps - anything except compared values, and it only swaps them when the - compare shows they are out of position. - */ - int pc_left, pc_right; - int u_right, u_left; - - int s; - - pc_left = ((part_left + part_right) / 2); - pc_right = pc_left; - u_right = pc_left - 1; - u_left = pc_right + 1; - - /* Qsort works best when the pivot value is also the median value - in the partition (unfortunately you can't find the median value - without first sorting :-), so to give the algorithm a helping - hand, we pick 3 elements and sort them and use the median value - of that tiny set as the pivot value. - - Some versions of qsort like to use the left middle and right as - the 3 elements to sort so they can insure the ends of the - partition will contain values which will stop the scan in the - compare loop, but when you have to call an arbitrarily complex - routine to do a compare, its really better to just keep track of - array index values to know when you hit the edge of the - partition and avoid the extra compare. An even better reason to - avoid using a compare call is the fact that you can drop off the - edge of the array if someone foolishly provides you with an - unstable compare function that doesn't always provide consistent - results. - - So, since it is simpler for us to compare the three adjacent - elements in the middle of the partition, those are the ones we - pick here (conveniently pointed at by u_right, pc_left, and - u_left). The values of the left, center, and right elements - are refered to as l c and r in the following comments. - */ - -#ifdef QSORT_ORDER_GUESS - swapped = 0; -#endif - s = qsort_cmp(u_right, pc_left); - if (s < 0) { - /* l < c */ - s = qsort_cmp(pc_left, u_left); - /* if l < c, c < r - already in order - nothing to do */ - if (s == 0) { - /* l < c, c == r - already in order, pc grows */ - ++pc_right; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else if (s > 0) { - /* l < c, c > r - need to know more */ - s = qsort_cmp(u_right, u_left); - if (s < 0) { - /* l < c, c > r, l < r - swap c & r to get ordered */ - qsort_swap(pc_left, u_left); - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else if (s == 0) { - /* l < c, c > r, l == r - swap c&r, grow pc */ - qsort_swap(pc_left, u_left); - --pc_left; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else { - /* l < c, c > r, l > r - make lcr into rlc to get ordered */ - qsort_rotate(pc_left, u_right, u_left); - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } - } - } else if (s == 0) { - /* l == c */ - s = qsort_cmp(pc_left, u_left); - if (s < 0) { - /* l == c, c < r - already in order, grow pc */ - --pc_left; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else if (s == 0) { - /* l == c, c == r - already in order, grow pc both ways */ - --pc_left; - ++pc_right; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else { - /* l == c, c > r - swap l & r, grow pc */ - qsort_swap(u_right, u_left); - ++pc_right; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } - } else { - /* l > c */ - s = qsort_cmp(pc_left, u_left); - if (s < 0) { - /* l > c, c < r - need to know more */ - s = qsort_cmp(u_right, u_left); - if (s < 0) { - /* l > c, c < r, l < r - swap l & c to get ordered */ - qsort_swap(u_right, pc_left); - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else if (s == 0) { - /* l > c, c < r, l == r - swap l & c, grow pc */ - qsort_swap(u_right, pc_left); - ++pc_right; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else { - /* l > c, c < r, l > r - rotate lcr into crl to order */ - qsort_rotate(u_right, pc_left, u_left); - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } - } else if (s == 0) { - /* l > c, c == r - swap ends, grow pc */ - qsort_swap(u_right, u_left); - --pc_left; - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } else { - /* l > c, c > r - swap ends to get in order */ - qsort_swap(u_right, u_left); - qsort_all_asserts(pc_left, pc_right, u_left + 1, u_right - 1); - } - } - /* We now know the 3 middle elements have been compared and - arranged in the desired order, so we can shrink the uncompared - sets on both sides - */ - --u_right; - ++u_left; - qsort_all_asserts(pc_left, pc_right, u_left, u_right); - - /* The above massive nested if was the simple part :-). We now have - the middle 3 elements ordered and we need to scan through the - uncompared sets on either side, swapping elements that are on - the wrong side or simply shuffling equal elements around to get - all equal elements into the pivot chunk. - */ - - for ( ; ; ) { - int still_work_on_left; - int still_work_on_right; - - /* Scan the uncompared values on the left. If I find a value - equal to the pivot value, move it over so it is adjacent to - the pivot chunk and expand the pivot chunk. If I find a value - less than the pivot value, then just leave it - its already - on the correct side of the partition. If I find a greater - value, then stop the scan. - */ - while ((still_work_on_left = (u_right >= part_left))) { - s = qsort_cmp(u_right, pc_left); - if (s < 0) { - --u_right; - } else if (s == 0) { - --pc_left; - if (pc_left != u_right) { - qsort_swap(u_right, pc_left); - } - --u_right; - } else { - break; - } - qsort_assert(u_right < pc_left); - qsort_assert(pc_left <= pc_right); - qsort_assert(qsort_cmp(u_right + 1, pc_left) <= 0); - qsort_assert(qsort_cmp(pc_left, pc_right) == 0); - } - /* Do a mirror image scan of uncompared values on the right - */ - while ((still_work_on_right = (u_left <= part_right))) { - s = qsort_cmp(pc_right, u_left); - if (s < 0) { - ++u_left; - } else if (s == 0) { - ++pc_right; - if (pc_right != u_left) { - qsort_swap(pc_right, u_left); - } - ++u_left; - } else { - break; - } - qsort_assert(u_left > pc_right); - qsort_assert(pc_left <= pc_right); - qsort_assert(qsort_cmp(pc_right, u_left - 1) <= 0); - qsort_assert(qsort_cmp(pc_left, pc_right) == 0); - } + /* Copy all the strictly low elements */ - if (still_work_on_left) { - /* I know I have a value on the left side which needs to be - on the right side, but I need to know more to decide - exactly the best thing to do with it. - */ - if (still_work_on_right) { - /* I know I have values on both side which are out of - position. This is a big win because I kill two birds - with one swap (so to speak). I can advance the - uncompared pointers on both sides after swapping both - of them into the right place. - */ - qsort_swap(u_right, u_left); - --u_right; - ++u_left; - qsort_all_asserts(pc_left, pc_right, u_left, u_right); - } else { - /* I have an out of position value on the left, but the - right is fully scanned, so I "slide" the pivot chunk - and any less-than values left one to make room for the - greater value over on the right. If the out of position - value is immediately adjacent to the pivot chunk (there - are no less-than values), I can do that with a swap, - otherwise, I have to rotate one of the less than values - into the former position of the out of position value - and the right end of the pivot chunk into the left end - (got all that?). - */ - --pc_left; - if (pc_left == u_right) { - qsort_swap(u_right, pc_right); - qsort_all_asserts(pc_left, pc_right-1, u_left, u_right-1); - } else { - qsort_rotate(u_right, pc_left, pc_right); - qsort_all_asserts(pc_left, pc_right-1, u_left, u_right-1); - } - --pc_right; - --u_right; - } - } else if (still_work_on_right) { - /* Mirror image of complex case above: I have an out of - position value on the right, but the left is fully - scanned, so I need to shuffle things around to make room - for the right value on the left. - */ - ++pc_right; - if (pc_right == u_left) { - qsort_swap(u_left, pc_left); - qsort_all_asserts(pc_left+1, pc_right, u_left+1, u_right); - } else { - qsort_rotate(pc_right, pc_left, u_left); - qsort_all_asserts(pc_left+1, pc_right, u_left+1, u_right); - } - ++pc_left; - ++u_left; - } else { - /* No more scanning required on either side of partition, - break out of loop and figure out next set of partitions - */ - break; - } - } - - /* The elements in the pivot chunk are now in the right place. They - will never move or be compared again. All I have to do is decide - what to do with the stuff to the left and right of the pivot - chunk. - - Notes on the QSORT_ORDER_GUESS ifdef code: - - 1. If I just built these partitions without swapping any (or - very many) elements, there is a chance that the elements are - already ordered properly (being properly ordered will - certainly result in no swapping, but the converse can't be - proved :-). - - 2. A (properly written) insertion sort will run faster on - already ordered data than qsort will. - - 3. Perhaps there is some way to make a good guess about - switching to an insertion sort earlier than partition size 6 - (for instance - we could save the partition size on the stack - and increase the size each time we find we didn't swap, thus - switching to insertion sort earlier for partitions with a - history of not swapping). - - 4. Naturally, if I just switch right away, it will make - artificial benchmarks with pure ascending (or descending) - data look really good, but is that a good reason in general? - Hard to say... - */ - -#ifdef QSORT_ORDER_GUESS - if (swapped < 3) { -#if QSORT_ORDER_GUESS == 1 - qsort_break_even = (part_right - part_left) + 1; -#endif -#if QSORT_ORDER_GUESS == 2 - qsort_break_even *= 2; -#endif -#if QSORT_ORDER_GUESS == 3 - int prev_break = qsort_break_even; - qsort_break_even *= qsort_break_even; - if (qsort_break_even < prev_break) { - qsort_break_even = (part_right - part_left) + 1; - } -#endif - } else { - qsort_break_even = QSORT_BREAK_EVEN; - } -#endif + if (q == f1) { + FROMTOUPTO(f2, tp2, t); + *tp2++ = *f1++; + } else { + FROMTOUPTO(f1, tp2, t); + *tp2++ = *f2++; + } + } - if (part_left < pc_left) { - /* There are elements on the left which need more processing. - Check the right as well before deciding what to do. - */ - if (pc_right < part_right) { - /* We have two partitions to be sorted. Stack the biggest one - and process the smallest one on the next iteration. This - minimizes the stack height by insuring that any additional - stack entries must come from the smallest partition which - (because it is smallest) will have the fewest - opportunities to generate additional stack entries. - */ - if ((part_right - pc_right) > (pc_left - part_left)) { - /* stack the right partition, process the left */ - partition_stack[next_stack_entry].left = pc_right + 1; - partition_stack[next_stack_entry].right = part_right; -#ifdef QSORT_ORDER_GUESS - partition_stack[next_stack_entry].qsort_break_even = qsort_break_even; -#endif - part_right = pc_left - 1; - } else { - /* stack the left partition, process the right */ - partition_stack[next_stack_entry].left = part_left; - partition_stack[next_stack_entry].right = pc_left - 1; -#ifdef QSORT_ORDER_GUESS - partition_stack[next_stack_entry].qsort_break_even = qsort_break_even; -#endif - part_left = pc_right + 1; - } - qsort_assert(next_stack_entry < QSORT_MAX_STACK); - ++next_stack_entry; - } else { - /* The elements on the left are the only remaining elements - that need sorting, arrange for them to be processed as the - next partition. - */ - part_right = pc_left - 1; - } - } else if (pc_right < part_right) { - /* There is only one chunk on the right to be sorted, make it - the new partition and loop back around. - */ - part_left = pc_right + 1; - } else { - /* This whole partition wound up in the pivot chunk, so - we need to get a new partition off the stack. - */ - if (next_stack_entry == 0) { - /* the stack is empty - we are done */ - break; - } - --next_stack_entry; - part_left = partition_stack[next_stack_entry].left; - part_right = partition_stack[next_stack_entry].right; -#ifdef QSORT_ORDER_GUESS - qsort_break_even = partition_stack[next_stack_entry].qsort_break_even; -#endif - } - } else { - /* This partition is too small to fool with qsort complexity, just - do an ordinary insertion sort to minimize overhead. - */ - int i; - /* Assume 1st element is in right place already, and start checking - at 2nd element to see where it should be inserted. - */ - for (i = part_left + 1; i <= part_right; ++i) { - int j; - /* Scan (backwards - just in case 'i' is already in right place) - through the elements already sorted to see if the ith element - belongs ahead of one of them. - */ - for (j = i - 1; j >= part_left; --j) { - if (qsort_cmp(i, j) >= 0) { - /* i belongs right after j - */ - break; - } - } - ++j; - if (j != i) { - /* Looks like we really need to move some things - */ - int k; - temp = array[i]; - for (k = i - 1; k >= j; --k) - array[k + 1] = array[k]; - array[j] = temp; - } - } - - /* That partition is now sorted, grab the next one, or get out - of the loop if there aren't any more. - */ - - if (next_stack_entry == 0) { - /* the stack is empty - we are done */ - break; - } - --next_stack_entry; - part_left = partition_stack[next_stack_entry].left; - part_right = partition_stack[next_stack_entry].right; -#ifdef QSORT_ORDER_GUESS - qsort_break_even = partition_stack[next_stack_entry].qsort_break_even; -#endif - } - } - /* Believe it or not, the array is sorted at this point! */ + /* Run out remaining list */ + if (f1 == l1) { + if (f2 < l2) FROMTOUPTO(f2, tp2, l2); + } else FROMTOUPTO(f1, tp2, l1); + p1 = NEXT(p1) = POTHER(tp2, list2, list1); + } + t = list1; + list1 = list2; + list2 = t; + last = PINDEX(list2, nmemb); + } + if (base == list2) { + last = PINDEX(list1, nmemb); + FROMTOUPTO(list1, list2, last); + } + Safefree(aux); + return; } diff --git a/t/op/runlevel.t b/t/op/runlevel.t index b6c128b..3140f02 100755 --- a/t/op/runlevel.t +++ b/t/op/runlevel.t @@ -176,11 +176,13 @@ print "bar reached\n"; EXPECT Can't "goto" out of a pseudo block at - line 2. ######## +%seen = (); sub sortfn { (split(/./, 'x'x10000))[0]; my (@y) = ( 4, 6, 5); @y = sort { $a <=> $b } @y; - print "sortfn ".join(', ', @y)."\n"; + my $t = "sortfn ".join(', ', @y)."\n"; + print $t if ($seen{$t}++ == 0); return $_[0] <=> $_[1]; } @x = ( 3, 2, 1 ); @@ -188,8 +190,6 @@ sub sortfn { print "---- ".join(', ', @x)."\n"; EXPECT sortfn 4, 5, 6 -sortfn 4, 5, 6 -sortfn 4, 5, 6 ---- 1, 2, 3 ######## @a = (3, 2, 1);