From c62bb3c5f9f2e8319cf54344a6d168fe95f62879 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Mon, 17 Aug 2020 21:31:56 +1200
Subject: [PATCH v5 1/2] Add sort_template.h for making fast sort functions.

Move our qsort implementation into a header that can be used to
define specialized functions for better performance.

Discussion: https://postgr.es/m/CA%2BhUKGKMQFVpjr106gRhwk6R-nXv0qOcTreZuQzxgpHESAL6dw%40mail.gmail.com
---
 src/include/lib/sort_template.h | 428 ++++++++++++++++++++++++++++++++
 1 file changed, 428 insertions(+)
 create mode 100644 src/include/lib/sort_template.h

diff --git a/src/include/lib/sort_template.h b/src/include/lib/sort_template.h
new file mode 100644
index 0000000000..a279bcf959
--- /dev/null
+++ b/src/include/lib/sort_template.h
@@ -0,0 +1,428 @@
+/*-------------------------------------------------------------------------
+ *
+ * sort_template.h
+ *
+ *	  A template for a sort algorithm that supports varying degrees of
+ *	  specialization.
+ *
+ * Copyright (c) 2020, PostgreSQL Global Development Group
+ *
+ * Usage notes:
+ *
+ *	  To generate functions specialized for a type, the following parameter
+ *	  macros should be #define'd before this file is included.
+ *
+ *	  - ST_SORT - the name of a sort function to be generated
+ *	  - ST_ELEMENT_TYPE - type of the referenced elements
+ *	  - ST_DECLARE - if defined the functions and types are declared
+ *	  - ST_DEFINE - if defined the functions and types are defined
+ *	  - ST_SCOPE - scope (e.g. extern, static inline) for functions
+ *
+ *	  Instead of ST_ELEMENT_TYPE, ST_ELEMENT_TYPE_VOID can be defined.  Then
+ *	  the generated functions will automatically gain an "element_size"
+ *	  parameter.  This allows us to generate a traditional qsort function.
+ *
+ *	  One of the following macros must be defined, to show how to compare
+ *	  elements.  The first two options are arbitrary expressions depending
+ *	  on whether an extra pass-through argument is desired, and the third
+ *	  option should be defined if the sort function should receive a
+ *	  function pointer at runtime.
+ *
+ * 	  - ST_COMPARE(a, b) - a simple comparison expression
+ *	  - ST_COMPARE(a, b, arg) - variant that takes an extra argument
+ *	  - ST_COMPARE_RUNTIME_POINTER - sort function takes a function pointer
+ *
+ *	  To say that the comparator and therefore also sort function should
+ *	  receive an extra pass-through argument, specify the type of the
+ *	  argument.
+ *
+ *	  - ST_COMPARE_ARG_TYPE - type of extra argument
+ *
+ *	  The prototype of the generated sort function is:
+ *
+ *	  void ST_SORT(ST_ELEMENT_TYPE *data, size_t n,
+ *				   [size_t element_size,]
+ *				   [ST_SORT_compare_function compare,]
+ *				   [ST_COMPARE_ARG_TYPE *arg]);
+ *
+ *	  ST_SORT_compare_function is a function pointer of the following type:
+ *
+ *	  int (*)(const ST_ELEMENT_TYPE *a, const ST_ELEMENT_TYPE *b,
+ *			  [ST_COMPARE_ARG_TYPE *arg])
+ *
+ * HISTORY
+ *
+ *	  Modifications from vanilla NetBSD source:
+ *	  - Add do ... while() macro fix
+ *	  - Remove __inline, _DIAGASSERTs, __P
+ *	  - Remove ill-considered "swap_cnt" switch to insertion sort, in favor
+ *		of a simple check for presorted input.
+ *	  - Take care to recurse on the smaller partition, to bound stack usage
+ *	  - Convert into a header that can generate specialized functions
+ *
+ * IDENTIFICATION
+ *		src/include/lib/sort_template.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/*	  $NetBSD: qsort.c,v 1.13 2003/08/07 16:43:42 agc Exp $   */
+
+/*-
+ * Copyright (c) 1992, 1993
+ *	  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. 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.
+ */
+
+/*
+ * Qsort routine based on J. L. Bentley and M. D. McIlroy,
+ * "Engineering a sort function",
+ * Software--Practice and Experience 23 (1993) 1249-1265.
+ *
+ * We have modified their original by adding a check for already-sorted
+ * input, which seems to be a win per discussions on pgsql-hackers around
+ * 2006-03-21.
+ *
+ * Also, we recurse on the smaller partition and iterate on the larger one,
+ * which ensures we cannot recurse more than log(N) levels (since the
+ * partition recursed to is surely no more than half of the input).  Bentley
+ * and McIlroy explicitly rejected doing this on the grounds that it's "not
+ * worth the effort", but we have seen crashes in the field due to stack
+ * overrun, so that judgment seems wrong.
+ */
+
+#define ST_MAKE_PREFIX(a) CppConcat(a,_)
+#define ST_MAKE_NAME(a,b) ST_MAKE_NAME_(ST_MAKE_PREFIX(a),b)
+#define ST_MAKE_NAME_(a,b) CppConcat(a,b)
+
+/*
+ * If the element type is void, we'll also need an element_size argument
+ * because we don't know the size.
+ */
+#ifdef ST_ELEMENT_TYPE_VOID
+#define ST_ELEMENT_TYPE void
+#define ST_SORT_PROTO_SIZE , size_t element_size
+#define ST_SORT_INVOKE_SIZE , element_size
+#else
+#define ST_SORT_PROTO_SIZE
+#define ST_SORT_INVOKE_SIZE
+#endif
+
+/*
+ * If the user wants to be able to pass in compare functions at runtime,
+ * we'll need to make that an argument of the sort and med3 functions.
+ */
+#ifdef ST_COMPARE_RUNTIME_POINTER
+/*
+ * The type of the comparator function pointer that ST_SORT will take, unless
+ * you've already declared a type name manually and want to use that instead of
+ * having a new one defined.
+ */
+#ifndef ST_COMPARATOR_TYPE_NAME
+#define ST_COMPARATOR_TYPE_NAME ST_MAKE_NAME(ST_SORT, compare_function)
+#endif
+#define ST_COMPARE compare
+#ifndef ST_COMPARE_ARG_TYPE
+#define ST_SORT_PROTO_COMPARE , ST_COMPARATOR_TYPE_NAME compare
+#define ST_SORT_INVOKE_COMPARE , compare
+#else
+#define ST_SORT_PROTO_COMPARE , ST_COMPARATOR_TYPE_NAME compare
+#define ST_SORT_INVOKE_COMPARE , compare
+#endif
+#else
+#define ST_SORT_PROTO_COMPARE
+#define ST_SORT_INVOKE_COMPARE
+#endif
+
+/*
+ * If the user wants to use a compare function or expression that takes an
+ * extra argument, we'll need to make that an argument of the sort, compare and
+ * med3 functions.
+ */
+#ifdef ST_COMPARE_ARG_TYPE
+#define ST_SORT_PROTO_ARG , ST_COMPARE_ARG_TYPE *arg
+#define ST_SORT_INVOKE_ARG , arg
+#else
+#define ST_SORT_PROTO_ARG
+#define ST_SORT_INVOKE_ARG
+#endif
+
+#ifdef ST_DECLARE
+
+#ifdef ST_COMPARE_RUNTIME_POINTER
+typedef int (*ST_COMPARATOR_TYPE_NAME)(const ST_ELEMENT_TYPE *,
+									   const ST_ELEMENT_TYPE *
+									   ST_SORT_PROTO_ARG);
+#endif
+
+/* Declare the sort function.  Note optional arguments at end. */
+ST_SCOPE void ST_SORT(ST_ELEMENT_TYPE *first, size_t n
+					  ST_SORT_PROTO_SIZE
+					  ST_SORT_PROTO_COMPARE
+					  ST_SORT_PROTO_ARG);
+
+#endif
+
+#ifdef ST_DEFINE
+
+/* sort private helper functions */
+#define ST_MED3 ST_MAKE_NAME(ST_SORT, med3)
+#define ST_SWAP ST_MAKE_NAME(ST_SORT, swap)
+#define ST_SWAPN ST_MAKE_NAME(ST_SORT, swapn)
+
+/* Users expecting to run very large sorts may need them to be interruptible. */
+#ifdef ST_CHECK_FOR_INTERRUPTS
+#define DO_CHECK_FOR_INTERRUPTS() CHECK_FOR_INTERRUPTS()
+#else
+#define DO_CHECK_FOR_INTERRUPTS()
+#endif
+
+/*
+ * Create wrapper macros that know how to invoke compare, med3 and sort with
+ * the right arguments.
+ */
+#ifdef ST_COMPARE_RUNTIME_POINTER
+#define DO_COMPARE(a_, b_) ST_COMPARE((a_), (b_) ST_SORT_INVOKE_ARG)
+#elif defined(ST_COMPARE_ARG_TYPE)
+#define DO_COMPARE(a_, b_) ST_COMPARE((a_), (b_), arg)
+#else
+#define DO_COMPARE(a_, b_) ST_COMPARE((a_), (b_))
+#endif
+#define DO_MED3(a_, b_, c_)												\
+	ST_MED3((a_), (b_), (c_)											\
+			ST_SORT_INVOKE_COMPARE										\
+			ST_SORT_INVOKE_ARG)
+#define DO_SORT(a_, n_)													\
+	ST_SORT((a_), (n_)													\
+			ST_SORT_INVOKE_SIZE											\
+			ST_SORT_INVOKE_COMPARE										\
+			ST_SORT_INVOKE_ARG)
+
+/*
+ * If we're working with void pointers, we'll use pointer arithmetic based on
+ * uint8, and use the runtime element_size to step through the array and swap
+ * elements.  Otherwise we'll work with ST_ELEMENT_TYPE.
+ */
+#ifndef ST_ELEMENT_TYPE_VOID
+#define ST_POINTER_TYPE ST_ELEMENT_TYPE
+#define ST_POINTER_STEP 1
+#define DO_SWAPN(a_, b_, n_) ST_SWAPN((a_), (b_), (n_))
+#define DO_SWAP(a_, b_) ST_SWAP((a_), (b_))
+#else
+#define ST_POINTER_TYPE uint8
+#define ST_POINTER_STEP element_size
+#define DO_SWAPN(a_, b_, n_) ST_SWAPN((a_), (b_), (n_))
+#define DO_SWAP(a_, b_) DO_SWAPN((a_), (b_), element_size)
+#endif
+
+/*
+ * Find the median of three values.  Currently, performance seems to be best
+ * if the the comparator is inlined here, but the med3 function is not inlined
+ * in the qsort function.
+ */
+static pg_noinline ST_ELEMENT_TYPE *
+ST_MED3(ST_ELEMENT_TYPE *a,
+		ST_ELEMENT_TYPE *b,
+		ST_ELEMENT_TYPE *c
+		ST_SORT_PROTO_COMPARE
+		ST_SORT_PROTO_ARG)
+{
+		return DO_COMPARE(a, b) < 0 ?
+		(DO_COMPARE(b, c) < 0 ? b : (DO_COMPARE(a, c) < 0 ? c : a))
+		: (DO_COMPARE(b, c) > 0 ? b : (DO_COMPARE(a, c) < 0 ? a : c));
+}
+
+static inline void
+ST_SWAP(ST_POINTER_TYPE *a, ST_POINTER_TYPE *b)
+{
+	ST_POINTER_TYPE tmp = *a;
+
+	*a = *b;
+	*b = tmp;
+}
+
+static inline void
+ST_SWAPN(ST_POINTER_TYPE *a, ST_POINTER_TYPE *b, size_t n)
+{
+	for (size_t i = 0; i < n; ++i)
+		ST_SWAP(&a[i], &b[i]);
+}
+
+/*
+ * Sort an array.
+ */
+ST_SCOPE void
+ST_SORT(ST_ELEMENT_TYPE *data, size_t n
+		ST_SORT_PROTO_SIZE
+		ST_SORT_PROTO_COMPARE
+		ST_SORT_PROTO_ARG)
+{
+	ST_POINTER_TYPE *a = (ST_POINTER_TYPE *) data,
+			   *pa,
+			   *pb,
+			   *pc,
+			   *pd,
+			   *pl,
+			   *pm,
+			   *pn;
+	size_t		d1,
+				d2;
+	int			r,
+				presorted;
+
+loop:
+	DO_CHECK_FOR_INTERRUPTS();
+	if (n < 7)
+	{
+		for (pm = a + ST_POINTER_STEP; pm < a + n * ST_POINTER_STEP;
+			 pm += ST_POINTER_STEP)
+			for (pl = pm; pl > a && DO_COMPARE(pl - ST_POINTER_STEP, pl) > 0;
+				 pl -= ST_POINTER_STEP)
+				DO_SWAP(pl, pl - ST_POINTER_STEP);
+		return;
+	}
+	presorted = 1;
+	for (pm = a + ST_POINTER_STEP; pm < a + n * ST_POINTER_STEP;
+		 pm += ST_POINTER_STEP)
+	{
+		DO_CHECK_FOR_INTERRUPTS();
+		if (DO_COMPARE(pm - ST_POINTER_STEP, pm) > 0)
+		{
+			presorted = 0;
+			break;
+		}
+	}
+	if (presorted)
+		return;
+	pm = a + (n / 2) * ST_POINTER_STEP;
+	if (n > 7)
+	{
+		pl = a;
+		pn = a + (n - 1) * ST_POINTER_STEP;
+		if (n > 40)
+		{
+			size_t		d = (n / 8) * ST_POINTER_STEP;
+
+			pl = DO_MED3(pl, pl + d, pl + 2 * d);
+			pm = DO_MED3(pm - d, pm, pm + d);
+			pn = DO_MED3(pn - 2 * d, pn - d, pn);
+		}
+		pm = DO_MED3(pl, pm, pn);
+	}
+	DO_SWAP(a, pm);
+	pa = pb = a + ST_POINTER_STEP;
+	pc = pd = a + (n - 1) * ST_POINTER_STEP;
+	for (;;)
+	{
+		while (pb <= pc && (r = DO_COMPARE(pb, a)) <= 0)
+		{
+			if (r == 0)
+			{
+				DO_SWAP(pa, pb);
+				pa += ST_POINTER_STEP;
+			}
+			pb += ST_POINTER_STEP;
+			DO_CHECK_FOR_INTERRUPTS();
+		}
+		while (pb <= pc && (r = DO_COMPARE(pc, a)) >= 0)
+		{
+			if (r == 0)
+			{
+				DO_SWAP(pc, pd);
+				pd -= ST_POINTER_STEP;
+			}
+			pc -= ST_POINTER_STEP;
+			DO_CHECK_FOR_INTERRUPTS();
+		}
+		if (pb > pc)
+			break;
+		DO_SWAP(pb, pc);
+		pb += ST_POINTER_STEP;
+		pc -= ST_POINTER_STEP;
+	}
+	pn = a + n * ST_POINTER_STEP;
+	d1 = Min(pa - a, pb - pa);
+	DO_SWAPN(a, pb - d1, d1);
+	d1 = Min(pd - pc, pn - pd - ST_POINTER_STEP);
+	DO_SWAPN(pb, pn - d1, d1);
+	d1 = pb - pa;
+	d2 = pd - pc;
+	if (d1 <= d2)
+	{
+		/* Recurse on left partition, then iterate on right partition */
+		if (d1 > ST_POINTER_STEP)
+			DO_SORT(a, d1 / ST_POINTER_STEP);
+		if (d2 > ST_POINTER_STEP)
+		{
+			/* Iterate rather than recurse to save stack space */
+			/* DO_SORT(pn - d2, d2 / ST_POINTER_STEP) */
+			a = pn - d2;
+			n = d2 / ST_POINTER_STEP;
+			goto loop;
+		}
+	}
+	else
+	{
+		/* Recurse on right partition, then iterate on left partition */
+		if (d2 > ST_POINTER_STEP)
+			DO_SORT(pn - d2, d2 / ST_POINTER_STEP);
+		if (d1 > ST_POINTER_STEP)
+		{
+			/* Iterate rather than recurse to save stack space */
+			/* DO_SORT(a, d1 / ST_POINTER_STEP) */
+			n = d1 / ST_POINTER_STEP;
+			goto loop;
+		}
+	}
+}
+#endif
+
+#undef DO_COMPARE
+#undef DO_MED3
+#undef DO_SORT
+#undef DO_SWAP
+#undef DO_SWAPN
+#undef ST_COMPARATOR_TYPE_NAME
+#undef ST_COMPARE
+#undef ST_COMPARE_ARG_TYPE
+#undef ST_COMPARE_RUNTIME_POINTER
+#undef ST_ELEMENT_TYPE
+#undef ST_ELEMENT_TYPE_VOID
+#undef ST_MAKE_NAME
+#undef ST_MAKE_NAME_
+#undef ST_MAKE_PREFIX
+#undef ST_MED3
+#undef ST_POINTER_STEP
+#undef ST_POINTER_TYPE
+#undef ST_SORT
+#undef ST_SORT_INVOKE_ARG
+#undef ST_SORT_INVOKE_COMPARE
+#undef ST_SORT_INVOKE_SIZE
+#undef ST_SORT_PROTO_ARG
+#undef ST_SORT_PROTO_COMPARE
+#undef ST_SORT_PROTO_SIZE
+#undef ST_SWAP
+#undef ST_SWAPN
-- 
2.25.1

