struct opslot: document a field better

[perl5.git] / pp_sort.c

/*    pp_sort.c
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
 *    2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 by Larry Wall and others
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 */

/*
 *   ...they shuffled back towards the rear of the line.  'No, not at the
 *   rear!' the slave-driver shouted.  'Three files up. And stay there...
 *
 *     [p.931 of _The Lord of the Rings_, VI/ii: "The Land of Shadow"]
 */

/* This file contains pp ("push/pop") functions that
 * execute the opcodes that make up a perl program. A typical pp function
 * expects to find its arguments on the stack, and usually pushes its
 * results onto the stack, hence the 'pp' terminology. Each OP structure
 * contains a pointer to the relevant pp_foo() function.
 *
 * This particular file just contains pp_sort(), which is complex
 * enough to merit its own file! See the other pp*.c files for the rest of
 * the pp_ functions.
 */

#include "EXTERN.h"
#define PERL_IN_PP_SORT_C
#include "perl.h"

#define sv_cmp_static Perl_sv_cmp
#define sv_cmp_locale_static Perl_sv_cmp_locale

#ifndef SMALLSORT
#define	SMALLSORT (200)
#endif

/* Flags for qsortsv and mergesortsv */
#define SORTf_DESC   1
#define SORTf_STABLE 2
#define SORTf_UNSTABLE 8

/*
 * The mergesort implementation is by Peter M. Mcilroy <pmcilroy@lucent.com>.
 *
 * The original code was written in conjunction with BSD Computer Software
 * Research Group at University of California, Berkeley.
 *
 * See also: "Optimistic Sorting and Information Theoretic Complexity"
 *           Peter McIlroy
 *           SODA (Fourth Annual ACM-SIAM Symposium on Discrete Algorithms),
 *           pp 467-474, Austin, Texas, 25-27 January 1993.
 *
 * The integration to Perl is by John P. Linderman <jpl.jpl@gmail.com>.
 *
 * The code can be distributed under the same terms as Perl itself.
 *
 */


typedef char * aptr;		/* pointer for arithmetic on sizes */
typedef SV * gptr;		/* pointers in our lists */

/* 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.
*/

/* Pointer types for arithmetic and storage and convenience casts */

#define	APTR(P)	((aptr)(P))
#define	GPTP(P)	((gptr *)(P))
#define GPPP(P) ((gptr **)(P))


/* byte offset from pointer P to (larger) pointer Q */
#define	BYTEOFF(P, Q) (APTR(Q) - APTR(P))

#define PSIZE sizeof(gptr)

/* If PSIZE is power of 2, make PSHIFT that power, if that helps */

#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

/* Pointer into other corresponding to pointer into this */
#define	POTHER(P, THIS, OTHER) GPTP(APTR(OTHER) + BYTEOFF(THIS,P))

#define FROMTOUPTO(src, dst, lim) do *dst++ = *src++; while(src<lim)


/* Runs are identified by a pointer in the auxiliary list.
** The pointer is at the start of the list,
** and it points to the start of the next list.
** NEXT is used as an lvalue, too.
*/

#define	NEXT(P)		(*GPPP(P))


/* PTHRESH is the minimum number of pairs with the same sense to justify
** checking for a run and extending it.  Note that PTHRESH counts PAIRS,
** not just elements, so PTHRESH == 8 means a run of 16.
*/

#define	PTHRESH (8)

/* 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 RTHRESH (6)


/*
** 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.
*/


static IV
dynprep(pTHX_ gptr *list1, gptr *list2, size_t nmemb, const SVCOMPARE_t cmp)
{
    I32 sense;
    gptr *b, *p, *q, *t, *p2;
    gptr *last, *r;
    IV runs = 0;

    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 */
		gptr *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); ++runs;
		if (sense)
		    while (b < --p) {
			const gptr c = *b;
			*b++ = *p;
			*p = c;
		    }
		p = savep;
	    }
	    while (q < p) {		/* simple pairs */
		p2 = NEXT(p2) = p2 + 2; ++runs;
		if (sense) {
		    const gptr c = *q++;
		    *(q-1) = *q;
		    *q++ = c;
		} else q += 2;
	    }
	    if (((b = p) == t) && ((t+1) == last)) {
		NEXT(p2) = p2 + 1; ++runs;
		b++;
	    }
	    q = r;
	} while (b < t);
	sense = !sense;
    }
    return runs;
}


/* The original merge sort, in use since 5.7, was as fast as, or faster than,
 * qsort on many platforms, but slower than qsort, conspicuously so,
 * on others.  The most likely explanation was platform-specific
 * differences in cache sizes and relative speeds.
 *
 * The quicksort divide-and-conquer algorithm guarantees that, as the
 * problem is subdivided into smaller and smaller parts, the parts
 * fit into smaller (and faster) caches.  So it doesn't matter how
 * many levels of cache exist, quicksort will "find" them, and,
 * as long as smaller is faster, take advantage of them.
 *
 * By contrast, consider how the original mergesort algorithm worked.
 * Suppose we have five runs (each typically of length 2 after dynprep).
 * 
 * pass               base                        aux
 *  0              1 2 3 4 5
 *  1                                           12 34 5
 *  2                1234 5
 *  3                                            12345
 *  4                 12345
 *
 * Adjacent pairs are merged in "grand sweeps" through the input.
 * This means, on pass 1, the records in runs 1 and 2 aren't revisited until
 * runs 3 and 4 are merged and the runs from run 5 have been copied.
 * The only cache that matters is one large enough to hold *all* the input.
 * On some platforms, this may be many times slower than smaller caches.
 *
 * The following pseudo-code uses the same basic merge algorithm,
 * but in a divide-and-conquer way.
 *
 * # merge $runs runs at offset $offset of list $list1 into $list2.
 * # all unmerged runs ($runs == 1) originate in list $base.
 * sub mgsort2 {
 *     my ($offset, $runs, $base, $list1, $list2) = @_;
 *
 *     if ($runs == 1) {
 *         if ($list1 is $base) copy run to $list2
 *         return offset of end of list (or copy)
 *     } else {
 *         $off2 = mgsort2($offset, $runs-($runs/2), $base, $list2, $list1)
 *         mgsort2($off2, $runs/2, $base, $list2, $list1)
 *         merge the adjacent runs at $offset of $list1 into $list2
 *         return the offset of the end of the merged runs
 *     }
 * }
 * mgsort2(0, $runs, $base, $aux, $base);
 *
 * For our 5 runs, the tree of calls looks like 
 *
 *           5
 *      3        2
 *   2     1   1   1
 * 1   1
 *
 * 1   2   3   4   5
 *
 * and the corresponding activity looks like
 *
 * copy runs 1 and 2 from base to aux
 * merge runs 1 and 2 from aux to base
 * (run 3 is where it belongs, no copy needed)
 * merge runs 12 and 3 from base to aux
 * (runs 4 and 5 are where they belong, no copy needed)
 * merge runs 4 and 5 from base to aux
 * merge runs 123 and 45 from aux to base
 *
 * Note that we merge runs 1 and 2 immediately after copying them,
 * while they are still likely to be in fast cache.  Similarly,
 * run 3 is merged with run 12 while it still may be lingering in cache.
 * This implementation should therefore enjoy much of the cache-friendly
 * behavior that quicksort does.  In addition, it does less copying
 * than the original mergesort implementation (only runs 1 and 2 are copied)
 * and the "balancing" of merges is better (merged runs comprise more nearly
 * equal numbers of original runs).
 *
 * The actual cache-friendly implementation will use a pseudo-stack
 * to avoid recursion, and will unroll processing of runs of length 2,
 * but it is otherwise similar to the recursive implementation.
 */

typedef struct {
    IV	offset;		/* offset of 1st of 2 runs at this level */
    IV	runs;		/* how many runs must be combined into 1 */
} off_runs;		/* pseudo-stack element */


static I32
cmp_desc(pTHX_ gptr const a, gptr const b)
{
    return -PL_sort_RealCmp(aTHX_ a, b);
}

/*
=for apidoc sortsv_flags

In-place sort an array of SV pointers with the given comparison routine,
with various SORTf_* flag options.

=cut
*/
void
Perl_sortsv_flags(pTHX_ gptr *base, size_t nmemb, SVCOMPARE_t cmp, U32 flags)
{
    IV i, run, offset;
    I32 sense, level;
    gptr *f1, *f2, *t, *b, *p;
    int iwhich;
    gptr *aux;
    gptr *p1;
    gptr small[SMALLSORT];
    gptr *which[3];
    off_runs stack[60], *stackp;
    SVCOMPARE_t savecmp = NULL;

    PERL_ARGS_ASSERT_SORTSV_FLAGS;
    if (nmemb <= 1) return;			/* sorted trivially */

    if ((flags & SORTf_DESC) != 0) {
	savecmp = PL_sort_RealCmp;	/* Save current comparison routine, if any */
	PL_sort_RealCmp = cmp;	/* Put comparison routine where cmp_desc can find it */
	cmp = cmp_desc;
    }

    if (nmemb <= SMALLSORT) aux = small;	/* use stack for aux array */
    else { Newx(aux,nmemb,gptr); }		/* allocate auxiliary array */
    level = 0;
    stackp = stack;
    stackp->runs = dynprep(aTHX_ base, aux, nmemb, cmp);
    stackp->offset = offset = 0;
    which[0] = which[2] = base;
    which[1] = aux;
    for (;;) {
	/* On levels where both runs have be constructed (stackp->runs == 0),
	 * merge them, and note the offset of their end, in case the offset
	 * is needed at the next level up.  Hop up a level, and,
	 * as long as stackp->runs is 0, keep merging.
	 */
	IV runs = stackp->runs;
	if (runs == 0) {
	    gptr *list1, *list2;
	    iwhich = level & 1;
	    list1 = which[iwhich];		/* area where runs are now */
	    list2 = which[++iwhich];		/* area for merged runs */
	    do {
		gptr *l1, *l2, *tp2;
		offset = stackp->offset;
		f1 = p1 = list1 + offset;		/* start of first run */
		p = tp2 = list2 + offset;	/* where merged run will go */
		t = NEXT(p);			/* where first run ends */
		f2 = l1 = POTHER(t, list2, list1); /* ... on the other side */
		t = NEXT(t);			/* where second runs ends */
		l2 = POTHER(t, list2, list1);	/* ... on the other side */
		offset = PNELEM(list2, 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.
		    */

		    gptr *q;
		    if (cmp(aTHX_ *f1, *f2) <= 0) {
			q = f2; b = f1; t = l1;
			sense = -1;
		    } else {
			q = f1; b = f2; t = l2;
			sense = 0;
		    }


		    /* 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;
		    }


		    /* 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.
		    */

		    b++;
		    while (b < t) {
			p = PINDEX(b, (PNELEM(b, t) - 1) / 2);
			if (cmp(aTHX_ *q, *p) <= sense) {
			    t = p;
			} else b = p + 1;
		    }


		    /* Copy all the strictly low elements */

		    if (q == f1) {
			FROMTOUPTO(f2, tp2, t);
			*tp2++ = *f1++;
		    } else {
			FROMTOUPTO(f1, tp2, t);
			*tp2++ = *f2++;
		    }
		}


		/* 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);

		if (--level == 0) goto done;
		--stackp;
		t = list1; list1 = list2; list2 = t;	/* swap lists */
	    } while ((runs = stackp->runs) == 0);
	}


	stackp->runs = 0;		/* current run will finish level */
	/* While there are more than 2 runs remaining,
	 * turn them into exactly 2 runs (at the "other" level),
	 * each made up of approximately half the runs.
	 * Stack the second half for later processing,
	 * and set about producing the first half now.
	 */
	while (runs > 2) {
	    ++level;
	    ++stackp;
	    stackp->offset = offset;
	    runs -= stackp->runs = runs / 2;
	}
	/* We must construct a single run from 1 or 2 runs.
	 * All the original runs are in which[0] == base.
	 * The run we construct must end up in which[level&1].
	 */
	iwhich = level & 1;
	if (runs == 1) {
	    /* Constructing a single run from a single run.
	     * If it's where it belongs already, there's nothing to do.
	     * Otherwise, copy it to where it belongs.
	     * A run of 1 is either a singleton at level 0,
	     * or the second half of a split 3.  In neither event
	     * is it necessary to set offset.  It will be set by the merge
	     * that immediately follows.
	     */
	    if (iwhich) {	/* Belongs in aux, currently in base */
		f1 = b = PINDEX(base, offset);	/* where list starts */
		f2 = PINDEX(aux, offset);	/* where list goes */
		t = NEXT(f2);			/* where list will end */
		offset = PNELEM(aux, t);	/* offset thereof */
		t = PINDEX(base, offset);	/* where it currently ends */
		FROMTOUPTO(f1, f2, t);		/* copy */
		NEXT(b) = t;			/* set up parallel pointer */
	    } else if (level == 0) goto done;	/* single run at level 0 */
	} else {
	    /* Constructing a single run from two runs.
	     * The merge code at the top will do that.
	     * We need only make sure the two runs are in the "other" array,
	     * so they'll end up in the correct array after the merge.
	     */
	    ++level;
	    ++stackp;
	    stackp->offset = offset;
	    stackp->runs = 0;	/* take care of both runs, trigger merge */
	    if (!iwhich) {	/* Merged runs belong in aux, copy 1st */
		f1 = b = PINDEX(base, offset);	/* where first run starts */
		f2 = PINDEX(aux, offset);	/* where it will be copied */
		t = NEXT(f2);			/* where first run will end */
		offset = PNELEM(aux, t);	/* offset thereof */
		p = PINDEX(base, offset);	/* end of first run */
		t = NEXT(t);			/* where second run will end */
		t = PINDEX(base, PNELEM(aux, t)); /* where it now ends */
		FROMTOUPTO(f1, f2, t);		/* copy both runs */
		NEXT(b) = p;			/* paralleled pointer for 1st */
		NEXT(p) = t;			/* ... and for second */
	    }
	}
    }
  done:
    if (aux != small) Safefree(aux);	/* free iff allocated */
    if (savecmp != NULL) {
	 PL_sort_RealCmp = savecmp;	/* Restore current comparison routine, if any */
    }
    return;
}

/*
 * The quicksort implementation 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

	b) the "Artistic License" which comes with this Kit.

   Details on the perl license can be found in the perl source code which
   may be located via the www.perl.com web page.

   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.

   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).

   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 :-).

   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...

   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 :-).
*/

/* ********************************************************** Configuration */

#ifndef QSORT_ORDER_GUESS
#define QSORT_ORDER_GUESS 2	/* Select doubling version of the netBSD trick */
#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

/* 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

/* QSORT_PLAY_SAFE is the size of the largest partition we're willing
   to go quadratic on.  We innoculate larger partitions against
   quadratic behavior by shuffling them before sorting.  This is not
   an absolute guarantee of non-quadratic behavior, but it would take
   staggeringly bad luck to pick extreme elements as the pivot
   from randomized data.
*/
#ifndef QSORT_PLAY_SAFE
#define QSORT_PLAY_SAFE 255
#endif

/* ************************************************************* Data Types */

/* hold left and right index values of a partition waiting to be sorted (the
   partition includes both left and right - right is NOT one past the end or
   anything like that).
*/
struct partition_stack_entry {
   int left;
   int right;
#ifdef QSORT_ORDER_GUESS
   int qsort_break_even;
#endif
};

/* ******************************************************* Shorthand Macros */

/* Note that these macros will be used from inside the qsort function where
   we happen to know that the variable 'elt_size' contains the size of an
   array element and the variable 'temp' points to enough space to hold a
   temp element and the variable 'array' points to the array being sorted
   and 'compare' is the pointer to the compare routine.

   Also note that there are very many highly architecture specific ways
   these might be sped up, but this is simply the most generally portable
   code I could think of.
*/

/* Return < 0 == 0 or > 0 as the value of elt1 is < elt2, == elt2, > elt2
*/
#define qsort_cmp(elt1, elt2) \
   ((*compare)(aTHX_ array[elt1], array[elt2]))

#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.
*/
#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 */

#ifdef QSORT_DEBUG

static void
break_here()
{
   return; /* good place to set a breakpoint */
}

#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)
{
   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);
   }
}

#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)

#define qsort_all_asserts(PC_LEFT, PC_RIGHT, U_LEFT, U_RIGHT) ((void)0)

#endif

/*
=head1 Array Manipulation Functions

=for apidoc sortsv

In-place sort an array of SV pointers with the given comparison routine.

Currently this always uses mergesort.  See C<L</sortsv_flags>> for a more
flexible routine.

=cut
*/

void
Perl_sortsv(pTHX_ SV **array, size_t nmemb, SVCOMPARE_t cmp)
{
    PERL_ARGS_ASSERT_SORTSV;

    sortsv_flags(array, nmemb, cmp, 0);
}

#define SvNSIOK(sv) ((SvFLAGS(sv) & SVf_NOK) || ((SvFLAGS(sv) & (SVf_IOK|SVf_IVisUV)) == SVf_IOK))
#define SvSIOK(sv) ((SvFLAGS(sv) & (SVf_IOK|SVf_IVisUV)) == SVf_IOK)
#define SvNSIV(sv) ( SvNOK(sv) ? SvNVX(sv) : ( SvSIOK(sv) ? SvIVX(sv) : sv_2nv(sv) ) )

PP(pp_sort)
{
    dSP; dMARK; dORIGMARK;
    SV **p1 = ORIGMARK+1, **p2;
    SSize_t max, i;
    AV* av = NULL;
    GV *gv;
    CV *cv = NULL;
    U8 gimme = GIMME_V;
    OP* const nextop = PL_op->op_next;
    I32 overloading = 0;
    bool hasargs = FALSE;
    bool copytmps;
    I32 is_xsub = 0;
    const U8 priv = PL_op->op_private;
    const U8 flags = PL_op->op_flags;
    U32 sort_flags = 0;
    void (*sortsvp)(pTHX_ SV **array, size_t nmemb, SVCOMPARE_t cmp, U32 flags)
      = Perl_sortsv_flags;
    I32 all_SIVs = 1;

    if ((priv & OPpSORT_DESCEND) != 0)
	sort_flags |= SORTf_DESC;
    if ((priv & OPpSORT_STABLE) != 0)
	sort_flags |= SORTf_STABLE;
    if ((priv & OPpSORT_UNSTABLE) != 0)
	sort_flags |= SORTf_UNSTABLE;

    if (gimme != G_ARRAY) {
	SP = MARK;
	EXTEND(SP,1);
	RETPUSHUNDEF;
    }

    ENTER;
    SAVEVPTR(PL_sortcop);
    if (flags & OPf_STACKED) {
	if (flags & OPf_SPECIAL) {
            OP *nullop = OpSIBLING(cLISTOP->op_first);  /* pass pushmark */
            assert(nullop->op_type == OP_NULL);
	    PL_sortcop = nullop->op_next;
	}
	else {
	    GV *autogv = NULL;
	    HV *stash;
	    cv = sv_2cv(*++MARK, &stash, &gv, GV_ADD);
	  check_cv:
	    if (cv && SvPOK(cv)) {
		const char * const proto = SvPV_nolen_const(MUTABLE_SV(cv));
		if (proto && strEQ(proto, "$$")) {
		    hasargs = TRUE;
		}
	    }
	    if (cv && CvISXSUB(cv) && CvXSUB(cv)) {
		is_xsub = 1;
	    }
	    else if (!(cv && CvROOT(cv))) {
		if (gv) {
		    goto autoload;
		}
		else if (!CvANON(cv) && (gv = CvGV(cv))) {
		  if (cv != GvCV(gv)) cv = GvCV(gv);
		 autoload:
		  if (!autogv && (
			autogv = gv_autoload_pvn(
			    GvSTASH(gv), GvNAME(gv), GvNAMELEN(gv),
			    GvNAMEUTF8(gv) ? SVf_UTF8 : 0
			)
		     )) {
		    cv = GvCVu(autogv);
		    goto check_cv;
		  }
		  else {
		    SV *tmpstr = sv_newmortal();
		    gv_efullname3(tmpstr, gv, NULL);
		    DIE(aTHX_ "Undefined sort subroutine \"%" SVf "\" called",
			SVfARG(tmpstr));
		  }
		}
		else {
		    DIE(aTHX_ "Undefined subroutine in sort");
		}
	    }

	    if (is_xsub)
		PL_sortcop = (OP*)cv;
	    else
		PL_sortcop = CvSTART(cv);
	}
    }
    else {
	PL_sortcop = NULL;
    }

    /* optimiser converts "@a = sort @a" to "sort \@a".  In this case,
     * push (@a) onto stack, then assign result back to @a at the end of
     * this function */
    if (priv & OPpSORT_INPLACE) {
	assert( MARK+1 == SP && *SP && SvTYPE(*SP) == SVt_PVAV);
	(void)POPMARK; /* remove mark associated with ex-OP_AASSIGN */
	av = MUTABLE_AV((*SP));
        if (SvREADONLY(av))
            Perl_croak_no_modify();
	max = AvFILL(av) + 1;
        MEXTEND(SP, max);
	if (SvMAGICAL(av)) {
	    for (i=0; i < max; i++) {
		SV **svp = av_fetch(av, i, FALSE);
		*SP++ = (svp) ? *svp : NULL;
	    }
	}
        else {
            SV **svp = AvARRAY(av);
            assert(svp || max == 0);
	    for (i = 0; i < max; i++)
                *SP++ = *svp++;
	}
        SP--;
        p1 = p2 = SP - (max-1);
    }
    else {
	p2 = MARK+1;
	max = SP - MARK;
   }

    /* shuffle stack down, removing optional initial cv (p1!=p2), plus
     * any nulls; also stringify or converting to integer or number as
     * required any args */
    copytmps = cBOOL(PL_sortcop);
    for (i=max; i > 0 ; i--) {
	if ((*p1 = *p2++)) {			/* Weed out nulls. */
	    if (copytmps && SvPADTMP(*p1)) {
		*p1 = sv_mortalcopy(*p1);
            }
	    SvTEMP_off(*p1);
	    if (!PL_sortcop) {
		if (priv & OPpSORT_NUMERIC) {
		    if (priv & OPpSORT_INTEGER) {
			if (!SvIOK(*p1))
			    (void)sv_2iv_flags(*p1, SV_GMAGIC|SV_SKIP_OVERLOAD);
		    }
		    else {
			if (!SvNSIOK(*p1))
			    (void)sv_2nv_flags(*p1, SV_GMAGIC|SV_SKIP_OVERLOAD);
			if (all_SIVs && !SvSIOK(*p1))
			    all_SIVs = 0;
		    }
		}
		else {
		    if (!SvPOK(*p1))
			(void)sv_2pv_flags(*p1, 0,
			    SV_GMAGIC|SV_CONST_RETURN|SV_SKIP_OVERLOAD);
		}
		if (SvAMAGIC(*p1))
		    overloading = 1;
	    }
	    p1++;
	}
	else
	    max--;
    }
    if (max > 1) {
	SV **start;
	if (PL_sortcop) {
	    PERL_CONTEXT *cx;
	    const bool oldcatch = CATCH_GET;
            I32 old_savestack_ix = PL_savestack_ix;

	    SAVEOP();

	    CATCH_SET(TRUE);
	    PUSHSTACKi(PERLSI_SORT);
	    if (!hasargs && !is_xsub) {
		SAVEGENERICSV(PL_firstgv);
		SAVEGENERICSV(PL_secondgv);
		PL_firstgv = MUTABLE_GV(SvREFCNT_inc(
		    gv_fetchpvs("a", GV_ADD|GV_NOTQUAL, SVt_PV)
		));
		PL_secondgv = MUTABLE_GV(SvREFCNT_inc(
		    gv_fetchpvs("b", GV_ADD|GV_NOTQUAL, SVt_PV)
		));
                /* make sure the GP isn't removed out from under us for
                 * the SAVESPTR() */
                save_gp(PL_firstgv, 0);
                save_gp(PL_secondgv, 0);
                /* we don't want modifications localized */
                GvINTRO_off(PL_firstgv);
                GvINTRO_off(PL_secondgv);
		SAVEGENERICSV(GvSV(PL_firstgv));
		SvREFCNT_inc(GvSV(PL_firstgv));
		SAVEGENERICSV(GvSV(PL_secondgv));
		SvREFCNT_inc(GvSV(PL_secondgv));
	    }

            gimme = G_SCALAR;
	    cx = cx_pushblock(CXt_NULL, gimme, PL_stack_base, old_savestack_ix);
	    if (!(flags & OPf_SPECIAL)) {
		cx->cx_type = CXt_SUB|CXp_MULTICALL;
		cx_pushsub(cx, cv, NULL, hasargs);
		if (!is_xsub) {
		    PADLIST * const padlist = CvPADLIST(cv);

		    if (++CvDEPTH(cv) >= 2)
			pad_push(padlist, CvDEPTH(cv));
		    PAD_SET_CUR_NOSAVE(padlist, CvDEPTH(cv));

		    if (hasargs) {
			/* This is mostly copied from pp_entersub */
			AV * const av = MUTABLE_AV(PAD_SVl(0));

			cx->blk_sub.savearray = GvAV(PL_defgv);
			GvAV(PL_defgv) = MUTABLE_AV(SvREFCNT_inc_simple(av));
		    }

		}
	    }

	    start = p1 - max;
	    sortsvp(aTHX_ start, max,
		    (is_xsub ? S_sortcv_xsub : hasargs ? S_sortcv_stacked : S_sortcv),
		    sort_flags);

            /* Reset cx, in case the context stack has been reallocated. */
            cx = CX_CUR();

	    PL_stack_sp = PL_stack_base + cx->blk_oldsp;

            CX_LEAVE_SCOPE(cx);
	    if (!(flags & OPf_SPECIAL)) {
                assert(CxTYPE(cx) == CXt_SUB);
                cx_popsub(cx);
	    }
            else
                assert(CxTYPE(cx) == CXt_NULL);
                /* there isn't a POPNULL ! */

	    cx_popblock(cx);
            CX_POP(cx);
	    POPSTACK;
	    CATCH_SET(oldcatch);
	}
	else {
	    MEXTEND(SP, 20);	/* Can't afford stack realloc on signal. */
	    start = ORIGMARK+1;
	    sortsvp(aTHX_ start, max,
		    (priv & OPpSORT_NUMERIC)
		        ? ( ( ( priv & OPpSORT_INTEGER) || all_SIVs)
			    ? ( overloading ? S_amagic_i_ncmp : S_sv_i_ncmp)
			    : ( overloading ? S_amagic_ncmp : S_sv_ncmp ) )
			: (
#ifdef USE_LOCALE_COLLATE
                           IN_LC_RUNTIME(LC_COLLATE)
			    ? ( overloading
				? (SVCOMPARE_t)S_amagic_cmp_locale
				: (SVCOMPARE_t)sv_cmp_locale_static)
                            :
#endif
			      ( overloading ? (SVCOMPARE_t)S_amagic_cmp : (SVCOMPARE_t)sv_cmp_static)),
		    sort_flags);
	}
	if ((priv & OPpSORT_REVERSE) != 0) {
	    SV **q = start+max-1;
	    while (start < q) {
		SV * const tmp = *start;
		*start++ = *q;
		*q-- = tmp;
	    }
	}
    }

    if (av) {
        /* copy back result to the array */
        SV** const base = MARK+1;
        if (SvMAGICAL(av)) {
            for (i = 0; i < max; i++)
                base[i] = newSVsv(base[i]);
            av_clear(av);
            av_extend(av, max);
            for (i=0; i < max; i++) {
                SV * const sv = base[i];
                SV ** const didstore = av_store(av, i, sv);
                if (SvSMAGICAL(sv))
                    mg_set(sv);
                if (!didstore)
                    sv_2mortal(sv);
            }
        }
        else {
            /* the elements of av are likely to be the same as the
             * (non-refcounted) elements on the stack, just in a different
             * order. However, its possible that someone's messed with av
             * in the meantime. So bump and unbump the relevant refcounts
             * first.
             */
            for (i = 0; i < max; i++) {
                SV *sv = base[i];
                assert(sv);
                if (SvREFCNT(sv) > 1)
                    base[i] = newSVsv(sv);
                else
                    SvREFCNT_inc_simple_void_NN(sv);
            }
            av_clear(av);
            if (max > 0) {
                av_extend(av, max);
                Copy(base, AvARRAY(av), max, SV*);
            }
            AvFILLp(av) = max - 1;
            AvREIFY_off(av);
            AvREAL_on(av);
        }
    }
    LEAVE;
    PL_stack_sp = ORIGMARK +  max;
    return nextop;
}

static I32
S_sortcv(pTHX_ SV *const a, SV *const b)
{
    const I32 oldsaveix = PL_savestack_ix;
    I32 result;
    PMOP * const pm = PL_curpm;
    COP * const cop = PL_curcop;
    SV *olda, *oldb;
 
    PERL_ARGS_ASSERT_SORTCV;

    olda = GvSV(PL_firstgv);
    GvSV(PL_firstgv) = SvREFCNT_inc_simple_NN(a);
    SvREFCNT_dec(olda);
    oldb = GvSV(PL_secondgv);
    GvSV(PL_secondgv) = SvREFCNT_inc_simple_NN(b);
    SvREFCNT_dec(oldb);
    PL_stack_sp = PL_stack_base;
    PL_op = PL_sortcop;
    CALLRUNOPS(aTHX);
    PL_curcop = cop;
    /* entry zero of a stack is always PL_sv_undef, which
     * simplifies converting a '()' return into undef in scalar context */
    assert(PL_stack_sp > PL_stack_base || *PL_stack_base == &PL_sv_undef);
    result = SvIV(*PL_stack_sp);

    LEAVE_SCOPE(oldsaveix);
    PL_curpm = pm;
    return result;
}

static I32
S_sortcv_stacked(pTHX_ SV *const a, SV *const b)
{
    const I32 oldsaveix = PL_savestack_ix;
    I32 result;
    AV * const av = GvAV(PL_defgv);
    PMOP * const pm = PL_curpm;
    COP * const cop = PL_curcop;

    PERL_ARGS_ASSERT_SORTCV_STACKED;

    if (AvREAL(av)) {
	av_clear(av);
	AvREAL_off(av);
	AvREIFY_on(av);
    }
    if (AvMAX(av) < 1) {
	SV **ary = AvALLOC(av);
	if (AvARRAY(av) != ary) {
	    AvMAX(av) += AvARRAY(av) - AvALLOC(av);
	    AvARRAY(av) = ary;
	}
	if (AvMAX(av) < 1) {
	    Renew(ary,2,SV*);
	    AvMAX(av) = 1;
	    AvARRAY(av) = ary;
	    AvALLOC(av) = ary;
	}
    }
    AvFILLp(av) = 1;

    AvARRAY(av)[0] = a;
    AvARRAY(av)[1] = b;
    PL_stack_sp = PL_stack_base;
    PL_op = PL_sortcop;
    CALLRUNOPS(aTHX);
    PL_curcop = cop;
    /* entry zero of a stack is always PL_sv_undef, which
     * simplifies converting a '()' return into undef in scalar context */
    assert(PL_stack_sp > PL_stack_base || *PL_stack_base == &PL_sv_undef);
    result = SvIV(*PL_stack_sp);

    LEAVE_SCOPE(oldsaveix);
    PL_curpm = pm;
    return result;
}

static I32
S_sortcv_xsub(pTHX_ SV *const a, SV *const b)
{
    dSP;
    const I32 oldsaveix = PL_savestack_ix;
    CV * const cv=MUTABLE_CV(PL_sortcop);
    I32 result;
    PMOP * const pm = PL_curpm;

    PERL_ARGS_ASSERT_SORTCV_XSUB;

    SP = PL_stack_base;
    PUSHMARK(SP);
    EXTEND(SP, 2);
    *++SP = a;
    *++SP = b;
    PUTBACK;
    (void)(*CvXSUB(cv))(aTHX_ cv);
    /* entry zero of a stack is always PL_sv_undef, which
     * simplifies converting a '()' return into undef in scalar context */
    assert(PL_stack_sp > PL_stack_base || *PL_stack_base == &PL_sv_undef);
    result = SvIV(*PL_stack_sp);

    LEAVE_SCOPE(oldsaveix);
    PL_curpm = pm;
    return result;
}


static I32
S_sv_ncmp(pTHX_ SV *const a, SV *const b)
{
    I32 cmp = do_ncmp(a, b);

    PERL_ARGS_ASSERT_SV_NCMP;

    if (cmp == 2) {
	if (ckWARN(WARN_UNINITIALIZED)) report_uninit(NULL);
	return 0;
    }

    return cmp;
}

static I32
S_sv_i_ncmp(pTHX_ SV *const a, SV *const b)
{
    const IV iv1 = SvIV(a);
    const IV iv2 = SvIV(b);

    PERL_ARGS_ASSERT_SV_I_NCMP;

    return iv1 < iv2 ? -1 : iv1 > iv2 ? 1 : 0;
}

#define tryCALL_AMAGICbin(left,right,meth) \
    (SvAMAGIC(left)||SvAMAGIC(right)) \
	? amagic_call(left, right, meth, 0) \
	: NULL;

#define SORT_NORMAL_RETURN_VALUE(val)  (((val) > 0) ? 1 : ((val) ? -1 : 0))

static I32
S_amagic_ncmp(pTHX_ SV *const a, SV *const b)
{
    SV * const tmpsv = tryCALL_AMAGICbin(a,b,ncmp_amg);

    PERL_ARGS_ASSERT_AMAGIC_NCMP;

    if (tmpsv) {
        if (SvIOK(tmpsv)) {
            const I32 i = SvIVX(tmpsv);
            return SORT_NORMAL_RETURN_VALUE(i);
        }
	else {
	    const NV d = SvNV(tmpsv);
	    return SORT_NORMAL_RETURN_VALUE(d);
	}
     }
     return S_sv_ncmp(aTHX_ a, b);
}

static I32
S_amagic_i_ncmp(pTHX_ SV *const a, SV *const b)
{
    SV * const tmpsv = tryCALL_AMAGICbin(a,b,ncmp_amg);

    PERL_ARGS_ASSERT_AMAGIC_I_NCMP;

    if (tmpsv) {
        if (SvIOK(tmpsv)) {
            const I32 i = SvIVX(tmpsv);
            return SORT_NORMAL_RETURN_VALUE(i);
        }
	else {
	    const NV d = SvNV(tmpsv);
	    return SORT_NORMAL_RETURN_VALUE(d);
	}
    }
    return S_sv_i_ncmp(aTHX_ a, b);
}

static I32
S_amagic_cmp(pTHX_ SV *const str1, SV *const str2)
{
    SV * const tmpsv = tryCALL_AMAGICbin(str1,str2,scmp_amg);

    PERL_ARGS_ASSERT_AMAGIC_CMP;

    if (tmpsv) {
        if (SvIOK(tmpsv)) {
            const I32 i = SvIVX(tmpsv);
            return SORT_NORMAL_RETURN_VALUE(i);
        }
	else {
	    const NV d = SvNV(tmpsv);
	    return SORT_NORMAL_RETURN_VALUE(d);
	}
    }
    return sv_cmp(str1, str2);
}

#ifdef USE_LOCALE_COLLATE

static I32
S_amagic_cmp_locale(pTHX_ SV *const str1, SV *const str2)
{
    SV * const tmpsv = tryCALL_AMAGICbin(str1,str2,scmp_amg);

    PERL_ARGS_ASSERT_AMAGIC_CMP_LOCALE;

    if (tmpsv) {
        if (SvIOK(tmpsv)) {
            const I32 i = SvIVX(tmpsv);
            return SORT_NORMAL_RETURN_VALUE(i);
        }
	else {
	    const NV d = SvNV(tmpsv);
	    return SORT_NORMAL_RETURN_VALUE(d);
	}
    }
    return sv_cmp_locale(str1, str2);
}

#endif

/*
 * ex: set ts=8 sts=4 sw=4 et:
 */