src/port/qsort_arg.c

   1 /*
   2  *      qsort_arg.c: qsort with a passthrough "void *" argument
   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  *        Take care to recurse on the smaller partition, to bound stack usage.
  10  *
  11  *      CAUTION: if you change this file, see also qsort.c, gen_qsort_tuple.pl
  12  *
  13  *      src/port/qsort_arg.c
  14  */
  15
  16 /*      $NetBSD: qsort.c,v 1.13 2003/08/07 16:43:42 agc Exp $   */
  17
  18 /*-
  19  * Copyright (c) 1992, 1993
  20  *      The Regents of the University of California.  All rights reserved.
  21  *
  22  * Redistribution and use in source and binary forms, with or without
  23  * modification, are permitted provided that the following conditions
  24  * are met:
  25  * 1. Redistributions of source code must retain the above copyright
  26  *        notice, this list of conditions and the following disclaimer.
  27  * 2. Redistributions in binary form must reproduce the above copyright
  28  *        notice, this list of conditions and the following disclaimer in the
  29  *        documentation and/or other materials provided with the distribution.
  30  * 3. Neither the name of the University nor the names of its contributors
  31  *        may be used to endorse or promote products derived from this software
  32  *        without specific prior written permission.
  33  *
  34  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  35  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  36  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  37  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  38  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  39  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  40  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  41  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  42  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  43  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  44  * SUCH DAMAGE.
  45  */
  46
  47 #include "c.h"
  48
  49
  50 static char *med3(char *a, char *b, char *c,
  51                                   qsort_arg_comparator cmp, void *arg);
  52 static void swapfunc(char *, char *, size_t, int);
  53
  54 /*
  55  * Qsort routine based on J. L. Bentley and M. D. McIlroy,
  56  * "Engineering a sort function",
  57  * Software--Practice and Experience 23 (1993) 1249-1265.
  58  *
  59  * We have modified their original by adding a check for already-sorted input,
  60  * which seems to be a win per discussions on pgsql-hackers around 2006-03-21.
  61  *
  62  * Also, we recurse on the smaller partition and iterate on the larger one,
  63  * which ensures we cannot recurse more than log(N) levels (since the
  64  * partition recursed to is surely no more than half of the input).  Bentley
  65  * and McIlroy explicitly rejected doing this on the grounds that it's "not
  66  * worth the effort", but we have seen crashes in the field due to stack
  67  * overrun, so that judgment seems wrong.
  68  */
  69
  70 #define swapcode(TYPE, parmi, parmj, n) \
  71 do {            \
  72         size_t i = (n) / sizeof (TYPE);                 \
  73         TYPE *pi = (TYPE *)(void *)(parmi);                     \
  74         TYPE *pj = (TYPE *)(void *)(parmj);                     \
  75         do {                                            \
  76                 TYPE    t = *pi;                        \
  77                 *pi++ = *pj;                            \
  78                 *pj++ = t;                              \
  79                 } while (--i > 0);                              \
  80 } while (0)
  81
  82 #define SWAPINIT(a, es) swaptype = ((char *)(a) - (char *)0) % sizeof(long) || \
  83         (es) % sizeof(long) ? 2 : (es) == sizeof(long)? 0 : 1
  84
  85 static void
  86 swapfunc(char *a, char *b, size_t n, int swaptype)
  87 {
  88         if (swaptype <= 1)
  89                 swapcode(long, a, b, n);
  90         else
  91                 swapcode(char, a, b, n);
  92 }
  93
  94 #define swap(a, b)                                              \
  95         if (swaptype == 0) {                                    \
  96                 long t = *(long *)(void *)(a);                  \
  97                 *(long *)(void *)(a) = *(long *)(void *)(b);    \
  98                 *(long *)(void *)(b) = t;                       \
  99         } else                                                  \
 100                 swapfunc(a, b, es, swaptype)
 101
 102 #define vecswap(a, b, n) if ((n) > 0) swapfunc(a, b, n, swaptype)
 103
 104 static char *
 105 med3(char *a, char *b, char *c, qsort_arg_comparator cmp, void *arg)
 106 {
 107         return cmp(a, b, arg) < 0 ?
 108                 (cmp(b, c, arg) < 0 ? b : (cmp(a, c, arg) < 0 ? c : a))
 109                 : (cmp(b, c, arg) > 0 ? b : (cmp(a, c, arg) < 0 ? a : c));
 110 }
 111
 112 void
 113 qsort_arg(void *a, size_t n, size_t es, qsort_arg_comparator cmp, void *arg)
 114 {
 115         char       *pa,
 116                            *pb,
 117                            *pc,
 118                            *pd,
 119                            *pl,
 120                            *pm,
 121                            *pn;
 122         size_t          d1,
 123                                 d2;
 124         int                     r,
 125                                 swaptype,
 126                                 presorted;
 127
 128 loop:SWAPINIT(a, es);
 129         if (n < 7)
 130         {
 131                 for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
 132                         for (pl = pm; pl > (char *) a && cmp(pl - es, pl, arg) > 0;
 133                                  pl -= es)
 134                                 swap(pl, pl - es);
 135                 return;
 136         }
 137         presorted = 1;
 138         for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
 139         {
 140                 if (cmp(pm - es, pm, arg) > 0)
 141                 {
 142                         presorted = 0;
 143                         break;
 144                 }
 145         }
 146         if (presorted)
 147                 return;
 148         pm = (char *) a + (n / 2) * es;
 149         if (n > 7)
 150         {
 151                 pl = (char *) a;
 152                 pn = (char *) a + (n - 1) * es;
 153                 if (n > 40)
 154                 {
 155                         size_t          d = (n / 8) * es;
 156
 157                         pl = med3(pl, pl + d, pl + 2 * d, cmp, arg);
 158                         pm = med3(pm - d, pm, pm + d, cmp, arg);
 159                         pn = med3(pn - 2 * d, pn - d, pn, cmp, arg);
 160                 }
 161                 pm = med3(pl, pm, pn, cmp, arg);
 162         }
 163         swap(a, pm);
 164         pa = pb = (char *) a + es;
 165         pc = pd = (char *) a + (n - 1) * es;
 166         for (;;)
 167         {
 168                 while (pb <= pc && (r = cmp(pb, a, arg)) <= 0)
 169                 {
 170                         if (r == 0)
 171                         {
 172                                 swap(pa, pb);
 173                                 pa += es;
 174                         }
 175                         pb += es;
 176                 }
 177                 while (pb <= pc && (r = cmp(pc, a, arg)) >= 0)
 178                 {
 179                         if (r == 0)
 180                         {
 181                                 swap(pc, pd);
 182                                 pd -= es;
 183                         }
 184                         pc -= es;
 185                 }
 186                 if (pb > pc)
 187                         break;
 188                 swap(pb, pc);
 189                 pb += es;
 190                 pc -= es;
 191         }
 192         pn = (char *) a + n * es;
 193         d1 = Min(pa - (char *) a, pb - pa);
 194         vecswap(a, pb - d1, d1);
 195         d1 = Min(pd - pc, pn - pd - es);
 196         vecswap(pb, pn - d1, d1);
 197         d1 = pb - pa;
 198         d2 = pd - pc;
 199         if (d1 <= d2)
 200         {
 201                 /* Recurse on left partition, then iterate on right partition */
 202                 if (d1 > es)
 203                         qsort_arg(a, d1 / es, es, cmp, arg);
 204                 if (d2 > es)
 205                 {
 206                         /* Iterate rather than recurse to save stack space */
 207                         /* qsort_arg(pn - d2, d2 / es, es, cmp, arg); */
 208                         a = pn - d2;
 209                         n = d2 / es;
 210                         goto loop;
 211                 }
 212         }
 213         else
 214         {
 215                 /* Recurse on right partition, then iterate on left partition */
 216                 if (d2 > es)
 217                         qsort_arg(pn - d2, d2 / es, es, cmp, arg);
 218                 if (d1 > es)
 219                 {
 220                         /* Iterate rather than recurse to save stack space */
 221                         /* qsort_arg(a, d1 / es, es, cmp, arg); */
 222                         n = d1 / es;
 223                         goto loop;
 224                 }
 225         }
 226 }