Postgres95 1.01 Distribution - Virgin SourcesPG95-1_01

1 files changed, 281 insertions, 0 deletions

diff --git a/src/backend/lib/qsort.c b/src/backend/lib/qsort.c
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+/*-------------------------------------------------------------------------
+ *
+ * qsort.c--
+ *    
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *    $Header: /cvsroot/pgsql/src/backend/lib/Attic/qsort.c,v 1.1.1.1 1996/07/09 06:21:29 scrappy Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+/*-
+ * Copyright (c) 1980, 1983, 1990 The Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. 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.
+ * 3. 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.
+ * 4. 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#if defined(LIBC_SCCS) && !defined(lint)
+static char sccsid[] = "@(#)qsort.c	5.9 (Berkeley) 2/23/91";
+#endif /* LIBC_SCCS and not lint */
+
+#include "postgres.h"
+#include "lib/qsort.h"
+
+/*
+ * MTHRESH is the smallest partition for which we compare for a median
+ * value instead of using the middle value.
+ */
+#define	MTHRESH	6
+
+/*
+ * THRESH is the minimum number of entries in a partition for continued
+ * partitioning.
+ */
+#define	THRESH	4
+
+static void insertion_sort(char* bot, int nmemb, int size, int (*compar)());
+static void quick_sort(char* bot, int nmemb, int size, int (*compar)());
+
+void pg_qsort(void *bot,
+	      size_t nmemb,
+	      size_t size, 
+	      int (*compar)(void *, void *))
+{
+
+	if (nmemb <= 1)
+		return;
+
+	if (nmemb >= THRESH)
+		quick_sort(bot, nmemb, size, compar);
+	else
+		insertion_sort(bot, nmemb, size, compar);
+}
+
+/*
+ * Swap two areas of size number of bytes.  Although qsort(3) permits random
+ * blocks of memory to be sorted, sorting pointers is almost certainly the
+ * common case (and, were it not, could easily be made so).  Regardless, it
+ * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
+ * arithmetic gets lost in the time required for comparison function calls.
+ */
+#define	SWAP(a, b) { \
+	cnt = size; \
+	do { \
+		ch = *a; \
+		*a++ = *b; \
+		*b++ = ch; \
+	} while (--cnt); \
+}
+
+/*
+ * Knuth, Vol. 3, page 116, Algorithm Q, step b, argues that a single pass
+ * of straight insertion sort after partitioning is complete is better than
+ * sorting each small partition as it is created.  This isn't correct in this
+ * implementation because comparisons require at least one (and often two)
+ * function calls and are likely to be the dominating expense of the sort.
+ * Doing a final insertion sort does more comparisons than are necessary
+ * because it compares the "edges" and medians of the partitions which are
+ * known to be already sorted.
+ *
+ * This is also the reasoning behind selecting a small THRESH value (see
+ * Knuth, page 122, equation 26), since the quicksort algorithm does less
+ * comparisons than the insertion sort.
+ */
+#define	SORT(bot, n) { \
+	if (n > 1) \
+		if (n == 2) { \
+			t1 = bot + size; \
+			if (compar(t1, bot) < 0) \
+				SWAP(t1, bot); \
+		} else \
+			insertion_sort(bot, n, size, compar); \
+}
+
+static void
+quick_sort(char* bot, int nmemb, int size, int (*compar)())
+{
+	register int cnt;
+	register u_char ch;
+	register char *top, *mid, *t1, *t2;
+	register int n1, n2;
+	char *bsv;
+
+	/* bot and nmemb must already be set. */
+partition:
+
+	/* find mid and top elements */
+	mid = bot + size * (nmemb >> 1);
+	top = bot + (nmemb - 1) * size;
+
+	/*
+	 * Find the median of the first, last and middle element (see Knuth,
+	 * Vol. 3, page 123, Eq. 28).  This test order gets the equalities
+	 * right.
+	 */
+	if (nmemb >= MTHRESH) {
+		n1 = compar(bot, mid);
+		n2 = compar(mid, top);
+		if (n1 < 0 && n2 > 0)
+			t1 = compar(bot, top) < 0 ? top : bot;
+		else if (n1 > 0 && n2 < 0)
+			t1 = compar(bot, top) > 0 ? top : bot;
+		else
+			t1 = mid;
+
+		/* if mid element not selected, swap selection there */
+		if (t1 != mid) {
+			SWAP(t1, mid);
+			mid -= size;
+		}
+	}
+
+	/* Standard quicksort, Knuth, Vol. 3, page 116, Algorithm Q. */
+#define	didswap	n1
+#define	newbot	t1
+#define	replace	t2
+	didswap = 0;
+	for (bsv = bot;;) {
+		for (; bot < mid && compar(bot, mid) <= 0; bot += size);
+		while (top > mid) {
+			if (compar(mid, top) <= 0) {
+				top -= size;
+				continue;
+			}
+			newbot = bot + size;	/* value of bot after swap */
+			if (bot == mid)		/* top <-> mid, mid == top */
+				replace = mid = top;
+			else {			/* bot <-> top */
+				replace = top;
+				top -= size;
+			}
+			goto swap;
+		}
+		if (bot == mid)
+			break;
+
+		/* bot <-> mid, mid == bot */
+		replace = mid;
+		newbot = mid = bot;		/* value of bot after swap */
+		top -= size;
+
+swap:		SWAP(bot, replace);
+		bot = newbot;
+		didswap = 1;
+	}
+
+	/*
+	 * Quicksort behaves badly in the presence of data which is already
+	 * sorted (see Knuth, Vol. 3, page 119) going from O N lg N to O N^2.
+	 * To avoid this worst case behavior, if a re-partitioning occurs
+	 * without swapping any elements, it is not further partitioned and
+	 * is insert sorted.  This wins big with almost sorted data sets and
+	 * only loses if the data set is very strangely partitioned.  A fix
+	 * for those data sets would be to return prematurely if the insertion
+	 * sort routine is forced to make an excessive number of swaps, and
+	 * continue the partitioning.
+	 */
+	if (!didswap) {
+		insertion_sort(bsv, nmemb, size, compar);
+		return;
+	}
+
+	/*
+	 * Re-partition or sort as necessary.  Note that the mid element
+	 * itself is correctly positioned and can be ignored.
+	 */
+#define	nlower	n1
+#define	nupper	n2
+	bot = bsv;
+	nlower = (mid - bot) / size;	/* size of lower partition */
+	mid += size;
+	nupper = nmemb - nlower - 1;	/* size of upper partition */
+
+	/*
+	 * If must call recursively, do it on the smaller partition; this
+	 * bounds the stack to lg N entries.
+	 */
+	if (nlower > nupper) {
+		if (nupper >= THRESH)
+			quick_sort(mid, nupper, size, compar);
+		else {
+			SORT(mid, nupper);
+			if (nlower < THRESH) {
+				SORT(bot, nlower);
+				return;
+			}
+		}
+		nmemb = nlower;
+	} else {
+		if (nlower >= THRESH)
+			quick_sort(bot, nlower, size, compar);
+		else {
+			SORT(bot, nlower);
+			if (nupper < THRESH) {
+				SORT(mid, nupper);
+				return;
+			}
+		}
+		bot = mid;
+		nmemb = nupper;
+	}
+	goto partition;
+}
+
+static void
+insertion_sort(char* bot, int nmemb, int size, int (*compar)())
+{
+	register int cnt;
+	register u_char ch;
+	register char *s1, *s2, *t1, *t2, *top;
+
+	/*
+	 * A simple insertion sort (see Knuth, Vol. 3, page 81, Algorithm
+	 * S).  Insertion sort has the same worst case as most simple sorts
+	 * (O N^2).  It gets used here because it is (O N) in the case of
+	 * sorted data.
+	 */
+	top = bot + nmemb * size;
+	for (t1 = bot + size; t1 < top;) {
+		for (t2 = t1; (t2 -= size) >= bot && compar(t1, t2) < 0;);
+		if (t1 != (t2 += size)) {
+			/* Bubble bytes up through each element. */
+			for (cnt = size; cnt--; ++t1) {
+				ch = *t1;
+				for (s1 = s2 = t1; (s2 -= size) >= t2; s1 = s2)
+					*s1 = *s2;
+				*s1 = ch;
+			}
+		} else
+			t1 += size;
+	}
+}