glib/gqsort.c

   1 /* GLIB - Library of useful routines for C programming
   2  * Copyright (C) 1991, 1992, 1996, 1997,1999,2004 Free Software Foundation, Inc.
   3  * Copyright (C) 2000 Eazel, Inc.
   4  * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2 of the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, write to the
  18  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19  * Boston, MA 02111-1307, USA.
  20  */
  21
  22 /*
  23  * This file was originally part of the GNU C Library, and was modified to allow
  24  * user data to be passed in to the sorting function.
  25  *
  26  * Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
  27  * Modified by Maciej Stachowiak (mjs@eazel.com)
  28  *
  29  * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
  30  * file for a list of people on the GLib Team.  See the ChangeLog
  31  * files for a list of changes.  These files are distributed with GLib
  32  * at ftp://ftp.gtk.org/pub/gtk/.
  33  */
  34
  35 #include "config.h"
  36
  37 #include <limits.h>
  38 #include <stdlib.h>
  39 #include <string.h>
  40
  41 #include "gqsort.h"
  42
  43 #include "gtestutils.h"
  44
  45 #ifdef HAVE_QSORT_R
  46
  47 /**
  48  * g_qsort_with_data:
  49  * @pbase: start of array to sort
  50  * @total_elems: elements in the array
  51  * @size: size of each element
  52  * @compare_func: function to compare elements
  53  * @user_data: data to pass to @compare_func
  54  *
  55  * This is just like the standard C qsort() function, but
  56  * the comparison routine accepts a user data argument.
  57  */
  58 void
  59 g_qsort_with_data (gconstpointer    pbase,
  60                    gint             total_elems,
  61                    gsize            size,
  62                    GCompareDataFunc compare_func,
  63                    gpointer         user_data)
  64 {
  65   qsort_r ((gpointer)pbase, total_elems, size, compare_func, user_data);
  66 }
  67
  68 #else
  69
  70 /* Byte-wise swap two items of size SIZE. */
  71 #define SWAP(a, b, size)                                                      \
  72   do                                                                          \
  73     {                                                                         \
  74       register size_t __size = (size);                                        \
  75       register char *__a = (a), *__b = (b);                                   \
  76       do                                                                      \
  77         {                                                                     \
  78           char __tmp = *__a;                                                  \
  79           *__a++ = *__b;                                                      \
  80           *__b++ = __tmp;                                                     \
  81         } while (--__size > 0);                                               \
  82     } while (0)
  83
  84 /* Discontinue quicksort algorithm when partition gets below this size.
  85    This particular magic number was chosen to work best on a Sun 4/260. */
  86 #define MAX_THRESH 4
  87
  88 /* Stack node declarations used to store unfulfilled partition obligations. */
  89 typedef struct
  90   {
  91     char *lo;
  92     char *hi;
  93   } stack_node;
  94
  95 /* The next 4 #defines implement a very fast in-line stack abstraction. */
  96 /* The stack needs log (total_elements) entries (we could even subtract
  97    log(MAX_THRESH)).  Since total_elements has type size_t, we get as
  98    upper bound for log (total_elements):
  99    bits per byte (CHAR_BIT) * sizeof(size_t).  */
 100 #define STACK_SIZE      (CHAR_BIT * sizeof(size_t))
 101 #define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
 102 #define POP(low, high)  ((void) (--top, (low = top->lo), (high = top->hi)))
 103 #define STACK_NOT_EMPTY (stack < top)
 104
 105
 106 /* Order size using quicksort.  This implementation incorporates
 107    four optimizations discussed in Sedgewick:
 108
 109    1. Non-recursive, using an explicit stack of pointer that store the
 110       next array partition to sort.  To save time, this maximum amount
 111       of space required to store an array of SIZE_MAX is allocated on the
 112       stack.  Assuming a 32-bit (64 bit) integer for size_t, this needs
 113       only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
 114       Pretty cheap, actually.
 115
 116    2. Chose the pivot element using a median-of-three decision tree.
 117       This reduces the probability of selecting a bad pivot value and
 118       eliminates certain extraneous comparisons.
 119
 120    3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
 121       insertion sort to order the MAX_THRESH items within each partition.
 122       This is a big win, since insertion sort is faster for small, mostly
 123       sorted array segments.
 124
 125    4. The larger of the two sub-partitions is always pushed onto the
 126       stack first, with the algorithm then concentrating on the
 127       smaller partition.  This *guarantees* no more than log (total_elems)
 128       stack size is needed (actually O(1) in this case)!  */
 129
 130 void
 131 g_qsort_with_data (gconstpointer    pbase,
 132                    gint             total_elems,
 133                    gsize            size,
 134                    GCompareDataFunc compare_func,
 135                    gpointer         user_data)
 136 {
 137   register char *base_ptr = (char *) pbase;
 138
 139   const size_t max_thresh = MAX_THRESH * size;
 140
 141   g_return_if_fail (total_elems >= 0);
 142   g_return_if_fail (pbase != NULL || total_elems == 0);
 143   g_return_if_fail (compare_func != NULL);
 144
 145   if (total_elems == 0)
 146     /* Avoid lossage with unsigned arithmetic below.  */
 147     return;
 148
 149   if (total_elems > MAX_THRESH)
 150     {
 151       char *lo = base_ptr;
 152       char *hi = &lo[size * (total_elems - 1)];
 153       stack_node stack[STACK_SIZE];
 154       stack_node *top = stack;
 155
 156       PUSH (NULL, NULL);
 157
 158       while (STACK_NOT_EMPTY)
 159         {
 160           char *left_ptr;
 161           char *right_ptr;
 162
 163           /* Select median value from among LO, MID, and HI. Rearrange
 164              LO and HI so the three values are sorted. This lowers the
 165              probability of picking a pathological pivot value and
 166              skips a comparison for both the LEFT_PTR and RIGHT_PTR in
 167              the while loops. */
 168
 169           char *mid = lo + size * ((hi - lo) / size >> 1);
 170
 171           if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
 172             SWAP (mid, lo, size);
 173           if ((*compare_func) ((void *) hi, (void *) mid, user_data) < 0)
 174             SWAP (mid, hi, size);
 175           else
 176             goto jump_over;
 177           if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
 178             SWAP (mid, lo, size);
 179         jump_over:;
 180
 181           left_ptr  = lo + size;
 182           right_ptr = hi - size;
 183
 184           /* Here's the famous ``collapse the walls'' section of quicksort.
 185              Gotta like those tight inner loops!  They are the main reason
 186              that this algorithm runs much faster than others. */
 187           do
 188             {
 189               while ((*compare_func) ((void *) left_ptr, (void *) mid, user_data) < 0)
 190                 left_ptr += size;
 191
 192               while ((*compare_func) ((void *) mid, (void *) right_ptr, user_data) < 0)
 193                 right_ptr -= size;
 194
 195               if (left_ptr < right_ptr)
 196                 {
 197                   SWAP (left_ptr, right_ptr, size);
 198                   if (mid == left_ptr)
 199                     mid = right_ptr;
 200                   else if (mid == right_ptr)
 201                     mid = left_ptr;
 202                   left_ptr += size;
 203                   right_ptr -= size;
 204                 }
 205               else if (left_ptr == right_ptr)
 206                 {
 207                   left_ptr += size;
 208                   right_ptr -= size;
 209                   break;
 210                 }
 211             }
 212           while (left_ptr <= right_ptr);
 213
 214           /* Set up pointers for next iteration.  First determine whether
 215              left and right partitions are below the threshold size.  If so,
 216              ignore one or both.  Otherwise, push the larger partition's
 217              bounds on the stack and continue sorting the smaller one. */
 218
 219           if ((size_t) (right_ptr - lo) <= max_thresh)
 220             {
 221               if ((size_t) (hi - left_ptr) <= max_thresh)
 222                 /* Ignore both small partitions. */
 223                 POP (lo, hi);
 224               else
 225                 /* Ignore small left partition. */
 226                 lo = left_ptr;
 227             }
 228           else if ((size_t) (hi - left_ptr) <= max_thresh)
 229             /* Ignore small right partition. */
 230             hi = right_ptr;
 231           else if ((right_ptr - lo) > (hi - left_ptr))
 232             {
 233               /* Push larger left partition indices. */
 234               PUSH (lo, right_ptr);
 235               lo = left_ptr;
 236             }
 237           else
 238             {
 239               /* Push larger right partition indices. */
 240               PUSH (left_ptr, hi);
 241               hi = right_ptr;
 242             }
 243         }
 244     }
 245
 246   /* Once the BASE_PTR array is partially sorted by quicksort the rest
 247      is completely sorted using insertion sort, since this is efficient
 248      for partitions below MAX_THRESH size. BASE_PTR points to the beginning
 249      of the array to sort, and END_PTR points at the very last element in
 250      the array (*not* one beyond it!). */
 251
 252 #define min(x, y) ((x) < (y) ? (x) : (y))
 253
 254   {
 255     char *const end_ptr = &base_ptr[size * (total_elems - 1)];
 256     char *tmp_ptr = base_ptr;
 257     char *thresh = min(end_ptr, base_ptr + max_thresh);
 258     register char *run_ptr;
 259
 260     /* Find smallest element in first threshold and place it at the
 261        array's beginning.  This is the smallest array element,
 262        and the operation speeds up insertion sort's inner loop. */
 263
 264     for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
 265       if ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr, user_data) < 0)
 266         tmp_ptr = run_ptr;
 267
 268     if (tmp_ptr != base_ptr)
 269       SWAP (tmp_ptr, base_ptr, size);
 270
 271     /* Insertion sort, running from left-hand-side up to right-hand-side.  */
 272
 273     run_ptr = base_ptr + size;
 274     while ((run_ptr += size) <= end_ptr)
 275       {
 276         tmp_ptr = run_ptr - size;
 277         while ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr, user_data) < 0)
 278           tmp_ptr -= size;
 279
 280         tmp_ptr += size;
 281         if (tmp_ptr != run_ptr)
 282           {
 283             char *trav;
 284
 285             trav = run_ptr + size;
 286             while (--trav >= run_ptr)
 287               {
 288                 char c = *trav;
 289                 char *hi, *lo;
 290
 291                 for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
 292                   *hi = *lo;
 293                 *hi = c;
 294               }
 295           }
 296       }
 297   }
 298 }
 299
 300 #endif /* HAVE_QSORT_R */