src/port/qsort.c

   1 /*
   2  *      qsort.c: standard quicksort algorithm
   3  *
   4  *      Modifications from vanilla NetBSD source:
   5  *        Add do ... while() macro fix
   6  *        Remove __inline, _DIAGASSERTs, __P
   7  *        Remove ill-considered "swap_cnt" switch to insertion sort,
   8  *        in favor of a simple check for presorted input.
   9  *
  10  *      CAUTION: if you change this file, see also qsort_arg.c
  11  *
  12  *      $PostgreSQL$
  13  */
  14
  15 /*      $NetBSD$        */
  16
  17 /*-
  18  * Copyright (c) 1992, 1993
  19  *      The Regents of the University of California.  All rights reserved.
  20  *
  21  * Redistribution and use in source and binary forms, with or without
  22  * modification, are permitted provided that the following conditions
  23  * are met:
  24  * 1. Redistributions of source code must retain the above copyright
  25  *        notice, this list of conditions and the following disclaimer.
  26  * 2. Redistributions in binary form must reproduce the above copyright
  27  *        notice, this list of conditions and the following disclaimer in the
  28  *        documentation and/or other materials provided with the distribution.
  29  * 3. Neither the name of the University nor the names of its contributors
  30  *        may be used to endorse or promote products derived from this software
  31  *        without specific prior written permission.
  32  *
  33  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  34  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  35  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  36  * ARE DISCLAIMED.      IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  37  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  38  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  39  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  40  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  41  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  42  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  43  * SUCH DAMAGE.
  44  */
  45
  46 #include "c.h"
  47
  48
  49 static char *med3(char *a, char *b, char *c,
  50          int (*cmp) (const void *, const void *));
  51 static void swapfunc(char *, char *, size_t, int);
  52
  53 /*
  54  * Qsort routine based on J. L. Bentley and M. D. McIlroy,
  55  * "Engineering a sort function",
  56  * Software--Practice and Experience 23 (1993) 1249-1265.
  57  * We have modified their original by adding a check for already-sorted input,
  58  * which seems to be a win per discussions on pgsql-hackers around 2006-03-21.
  59  */
  60 #define swapcode(TYPE, parmi, parmj, n) \
  61 do {            \
  62         size_t i = (n) / sizeof (TYPE);                 \
  63         TYPE *pi = (TYPE *)(void *)(parmi);                     \
  64         TYPE *pj = (TYPE *)(void *)(parmj);                     \
  65         do {                                            \
  66                 TYPE    t = *pi;                        \
  67                 *pi++ = *pj;                            \
  68                 *pj++ = t;                              \
  69                 } while (--i > 0);                              \
  70 } while (0)
  71
  72 #define SWAPINIT(a, es) swaptype = ((char *)(a) - (char *)0) % sizeof(long) || \
  73         (es) % sizeof(long) ? 2 : (es) == sizeof(long)? 0 : 1;
  74
  75 static void
  76 swapfunc(char *a, char *b, size_t n, int swaptype)
  77 {
  78         if (swaptype <= 1)
  79                 swapcode(long, a, b, n);
  80         else
  81                 swapcode(char, a, b, n);
  82 }
  83
  84 #define swap(a, b)                                              \
  85         if (swaptype == 0) {                                    \
  86                 long t = *(long *)(void *)(a);                  \
  87                 *(long *)(void *)(a) = *(long *)(void *)(b);    \
  88                 *(long *)(void *)(b) = t;                       \
  89         } else                                                  \
  90                 swapfunc(a, b, es, swaptype)
  91
  92 #define vecswap(a, b, n) if ((n) > 0) swapfunc((a), (b), (size_t)(n), swaptype)
  93
  94 static char *
  95 med3(char *a, char *b, char *c, int (*cmp) (const void *, const void *))
  96 {
  97         return cmp(a, b) < 0 ?
  98                 (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a))
  99                 : (cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c));
 100 }
 101
 102 void
 103 pg_qsort(void *a, size_t n, size_t es, int (*cmp) (const void *, const void *))
 104 {
 105         char       *pa,
 106                            *pb,
 107                            *pc,
 108                            *pd,
 109                            *pl,
 110                            *pm,
 111                            *pn;
 112         int                     d,
 113                                 r,
 114                                 swaptype,
 115                                 presorted;
 116
 117 loop:SWAPINIT(a, es);
 118         if (n < 7)
 119         {
 120                 for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
 121                         for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
 122                                  pl -= es)
 123                                 swap(pl, pl - es);
 124                 return;
 125         }
 126         presorted = 1;
 127         for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
 128         {
 129                 if (cmp(pm - es, pm) > 0)
 130                 {
 131                         presorted = 0;
 132                         break;
 133                 }
 134         }
 135         if (presorted)
 136                 return;
 137         pm = (char *) a + (n / 2) * es;
 138         if (n > 7)
 139         {
 140                 pl = (char *) a;
 141                 pn = (char *) a + (n - 1) * es;
 142                 if (n > 40)
 143                 {
 144                         d = (n / 8) * es;
 145                         pl = med3(pl, pl + d, pl + 2 * d, cmp);
 146                         pm = med3(pm - d, pm, pm + d, cmp);
 147                         pn = med3(pn - 2 * d, pn - d, pn, cmp);
 148                 }
 149                 pm = med3(pl, pm, pn, cmp);
 150         }
 151         swap(a, pm);
 152         pa = pb = (char *) a + es;
 153         pc = pd = (char *) a + (n - 1) * es;
 154         for (;;)
 155         {
 156                 while (pb <= pc && (r = cmp(pb, a)) <= 0)
 157                 {
 158                         if (r == 0)
 159                         {
 160                                 swap(pa, pb);
 161                                 pa += es;
 162                         }
 163                         pb += es;
 164                 }
 165                 while (pb <= pc && (r = cmp(pc, a)) >= 0)
 166                 {
 167                         if (r == 0)
 168                         {
 169                                 swap(pc, pd);
 170                                 pd -= es;
 171                         }
 172                         pc -= es;
 173                 }
 174                 if (pb > pc)
 175                         break;
 176                 swap(pb, pc);
 177                 pb += es;
 178                 pc -= es;
 179         }
 180         pn = (char *) a + n * es;
 181         r = Min(pa - (char *) a, pb - pa);
 182         vecswap(a, pb - r, r);
 183         r = Min(pd - pc, pn - pd - es);
 184         vecswap(pb, pn - r, r);
 185         if ((r = pb - pa) > es)
 186                 qsort(a, r / es, es, cmp);
 187         if ((r = pd - pc) > es)
 188         {
 189                 /* Iterate rather than recurse to save stack space */
 190                 a = pn - r;
 191                 n = r / es;
 192                 goto loop;
 193         }
 194 /*              qsort(pn - r, r / es, es, cmp);*/
 195 }