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 /* Byte-wise swap two items of size SIZE. */
  46 #define SWAP(a, b, size)                                                      \
  47   do                                                                          \
  48     {                                                                         \
  49       register size_t __size = (size);                                        \
  50       register char *__a = (a), *__b = (b);                                   \
  51       do                                                                      \
  52         {                                                                     \
  53           char __tmp = *__a;                                                  \
  54           *__a++ = *__b;                                                      \
  55           *__b++ = __tmp;                                                     \
  56         } while (--__size > 0);                                               \
  57     } while (0)
  58
  59 /* Discontinue quicksort algorithm when partition gets below this size.
  60    This particular magic number was chosen to work best on a Sun 4/260. */
  61 #define MAX_THRESH 4
  62
  63 /* Stack node declarations used to store unfulfilled partition obligations. */
  64 typedef struct
  65   {
  66     char *lo;
  67     char *hi;
  68   } stack_node;
  69
  70 /* The next 4 #defines implement a very fast in-line stack abstraction. */
  71 /* The stack needs log (total_elements) entries (we could even subtract
  72    log(MAX_THRESH)).  Since total_elements has type size_t, we get as
  73    upper bound for log (total_elements):
  74    bits per byte (CHAR_BIT) * sizeof(size_t).  */
  75 #define STACK_SIZE      (CHAR_BIT * sizeof(size_t))
  76 #define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
  77 #define POP(low, high)  ((void) (--top, (low = top->lo), (high = top->hi)))
  78 #define STACK_NOT_EMPTY (stack < top)
  79
  80
  81 /* Order size using quicksort.  This implementation incorporates
  82    four optimizations discussed in Sedgewick:
  83
  84    1. Non-recursive, using an explicit stack of pointer that store the
  85       next array partition to sort.  To save time, this maximum amount
  86       of space required to store an array of SIZE_MAX is allocated on the
  87       stack.  Assuming a 32-bit (64 bit) integer for size_t, this needs
  88       only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
  89       Pretty cheap, actually.
  90
  91    2. Chose the pivot element using a median-of-three decision tree.
  92       This reduces the probability of selecting a bad pivot value and
  93       eliminates certain extraneous comparisons.
  94
  95    3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
  96       insertion sort to order the MAX_THRESH items within each partition.
  97       This is a big win, since insertion sort is faster for small, mostly
  98       sorted array segments.
  99
 100    4. The larger of the two sub-partitions is always pushed onto the
 101       stack first, with the algorithm then concentrating on the
 102       smaller partition.  This *guarantees* no more than log (total_elems)
 103       stack size is needed (actually O(1) in this case)!  */
 104
 105 /**
 106  * g_qsort_with_data:
 107  * @pbase: start of array to sort
 108  * @total_elems: elements in the array
 109  * @size: size of each element
 110  * @compare_func: function to compare elements
 111  * @user_data: data to pass to @compare_func
 112  *
 113  * This is just like the standard C qsort() function, but
 114  * the comparison routine accepts a user data argument.
 115  *
 116  **/
 117 void
 118 g_qsort_with_data (gconstpointer    pbase,
 119                    gint             total_elems,
 120                    gsize            size,
 121                    GCompareDataFunc compare_func,
 122                    gpointer         user_data)
 123 {
 124   register char *base_ptr = (char *) pbase;
 125
 126   const size_t max_thresh = MAX_THRESH * size;
 127
 128   g_return_if_fail (total_elems >= 0);
 129   g_return_if_fail (pbase != NULL || total_elems == 0);
 130   g_return_if_fail (compare_func != NULL);
 131
 132   if (total_elems == 0)
 133     /* Avoid lossage with unsigned arithmetic below.  */
 134     return;
 135
 136   if (total_elems > MAX_THRESH)
 137     {
 138       char *lo = base_ptr;
 139       char *hi = &lo[size * (total_elems - 1)];
 140       stack_node stack[STACK_SIZE];
 141       stack_node *top = stack;
 142
 143       PUSH (NULL, NULL);
 144
 145       while (STACK_NOT_EMPTY)
 146         {
 147           char *left_ptr;
 148           char *right_ptr;
 149
 150           /* Select median value from among LO, MID, and HI. Rearrange
 151              LO and HI so the three values are sorted. This lowers the
 152              probability of picking a pathological pivot value and
 153              skips a comparison for both the LEFT_PTR and RIGHT_PTR in
 154              the while loops. */
 155
 156           char *mid = lo + size * ((hi - lo) / size >> 1);
 157
 158           if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
 159             SWAP (mid, lo, size);
 160           if ((*compare_func) ((void *) hi, (void *) mid, user_data) < 0)
 161             SWAP (mid, hi, size);
 162           else
 163             goto jump_over;
 164           if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
 165             SWAP (mid, lo, size);
 166         jump_over:;
 167
 168           left_ptr  = lo + size;
 169           right_ptr = hi - size;
 170
 171           /* Here's the famous ``collapse the walls'' section of quicksort.
 172              Gotta like those tight inner loops!  They are the main reason
 173              that this algorithm runs much faster than others. */
 174           do
 175             {
 176               while ((*compare_func) ((void *) left_ptr, (void *) mid, user_data) < 0)
 177                 left_ptr += size;
 178
 179               while ((*compare_func) ((void *) mid, (void *) right_ptr, user_data) < 0)
 180                 right_ptr -= size;
 181
 182               if (left_ptr < right_ptr)
 183                 {
 184                   SWAP (left_ptr, right_ptr, size);
 185                   if (mid == left_ptr)
 186                     mid = right_ptr;
 187                   else if (mid == right_ptr)
 188                     mid = left_ptr;
 189                   left_ptr += size;
 190                   right_ptr -= size;
 191                 }
 192               else if (left_ptr == right_ptr)
 193                 {
 194                   left_ptr += size;
 195                   right_ptr -= size;
 196                   break;
 197                 }
 198             }
 199           while (left_ptr <= right_ptr);
 200
 201           /* Set up pointers for next iteration.  First determine whether
 202              left and right partitions are below the threshold size.  If so,
 203              ignore one or both.  Otherwise, push the larger partition's
 204              bounds on the stack and continue sorting the smaller one. */
 205
 206           if ((size_t) (right_ptr - lo) <= max_thresh)
 207             {
 208               if ((size_t) (hi - left_ptr) <= max_thresh)
 209                 /* Ignore both small partitions. */
 210                 POP (lo, hi);
 211               else
 212                 /* Ignore small left partition. */
 213                 lo = left_ptr;
 214             }
 215           else if ((size_t) (hi - left_ptr) <= max_thresh)
 216             /* Ignore small right partition. */
 217             hi = right_ptr;
 218           else if ((right_ptr - lo) > (hi - left_ptr))
 219             {
 220               /* Push larger left partition indices. */
 221               PUSH (lo, right_ptr);
 222               lo = left_ptr;
 223             }
 224           else
 225             {
 226               /* Push larger right partition indices. */
 227               PUSH (left_ptr, hi);
 228               hi = right_ptr;
 229             }
 230         }
 231     }
 232
 233   /* Once the BASE_PTR array is partially sorted by quicksort the rest
 234      is completely sorted using insertion sort, since this is efficient
 235      for partitions below MAX_THRESH size. BASE_PTR points to the beginning
 236      of the array to sort, and END_PTR points at the very last element in
 237      the array (*not* one beyond it!). */
 238
 239 #define min(x, y) ((x) < (y) ? (x) : (y))
 240
 241   {
 242     char *const end_ptr = &base_ptr[size * (total_elems - 1)];
 243     char *tmp_ptr = base_ptr;
 244     char *thresh = min(end_ptr, base_ptr + max_thresh);
 245     register char *run_ptr;
 246
 247     /* Find smallest element in first threshold and place it at the
 248        array's beginning.  This is the smallest array element,
 249        and the operation speeds up insertion sort's inner loop. */
 250
 251     for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
 252       if ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr, user_data) < 0)
 253         tmp_ptr = run_ptr;
 254
 255     if (tmp_ptr != base_ptr)
 256       SWAP (tmp_ptr, base_ptr, size);
 257
 258     /* Insertion sort, running from left-hand-side up to right-hand-side.  */
 259
 260     run_ptr = base_ptr + size;
 261     while ((run_ptr += size) <= end_ptr)
 262       {
 263         tmp_ptr = run_ptr - size;
 264         while ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr, user_data) < 0)
 265           tmp_ptr -= size;
 266
 267         tmp_ptr += size;
 268         if (tmp_ptr != run_ptr)
 269           {
 270             char *trav;
 271
 272             trav = run_ptr + size;
 273             while (--trav >= run_ptr)
 274               {
 275                 char c = *trav;
 276                 char *hi, *lo;
 277
 278                 for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
 279                   *hi = *lo;
 280                 *hi = c;
 281               }
 282           }
 283       }
 284   }
 285 }