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postgresql/src/include/lib/sort_template.h

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/*-------------------------------------------------------------------------
*
* sort_template.h
*
* A template for a sort algorithm that supports varying degrees of
* specialization.
*
* Copyright (c) 2021-2024, PostgreSQL Global Development Group
* Portions Copyright (c) 1992-1994, Regents of the University of California
*
* 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
* - ST_CHECK_FOR_INTERRUPTS - if defined the sort is interruptible
*
* 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
*
* NB: If the comparator function is inlined, some compilers may produce
* worse code with the optimized comparison routines in common/int.h than
* with code with the following form:
*
* if (a < b)
* return -1;
* if (a > b)
* return 1;
* return 0;
*
* 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_ELEMENT_SIZE , size_t element_size
#define ST_SORT_INVOKE_ELEMENT_SIZE , element_size
#else
#define ST_SORT_PROTO_ELEMENT_SIZE
#define ST_SORT_INVOKE_ELEMENT_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_ELEMENT_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_ELEMENT_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 comparator is inlined here, but the med3 function is not inlined
* in the qsort function.
*
* Refer to the comment at the top of this file for known caveats to consider
* when writing inlined comparator functions.
*/
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_ELEMENT_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_CHECK_FOR_INTERRUPTS
#undef DO_COMPARE
#undef DO_MED3
#undef DO_SORT
#undef DO_SWAP
#undef DO_SWAPN
#undef ST_CHECK_FOR_INTERRUPTS
#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_SCOPE
#undef ST_SORT
#undef ST_SORT_INVOKE_ARG
#undef ST_SORT_INVOKE_COMPARE
#undef ST_SORT_INVOKE_ELEMENT_SIZE
#undef ST_SORT_PROTO_ARG
#undef ST_SORT_PROTO_COMPARE
#undef ST_SORT_PROTO_ELEMENT_SIZE
#undef ST_SWAP
#undef ST_SWAPN
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