source: trunk/third/glib2/glib/gqsort.c @ 20721

/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1991, 1992, 1996, 1997 Free Software Foundation, Inc.
 * Copyright (C) 2000 Eazel, Inc.
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * This file was originally part of the GNU C Library, and was modified to allow
 * user data to be passed in to the sorting function.
 *
 * Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
 * Modified by Maciej Stachowiak (mjs@eazel.com)
 *
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with GLib
 * at ftp://ftp.gtk.org/pub/gtk/.
 */

#include "config.h"

#include <string.h>

#include "glib.h"


/* Byte-wise swap two items of size SIZE. */
#define SWAP(a, b, size)                                                      \
  do                                                                          \
    {                                                                         \
      register size_t __size = (size);                                        \
      register char *__a = (a), *__b = (b);                                   \
      do                                                                      \
        {                                                                     \
          char __tmp = *__a;                                                  \
          *__a++ = *__b;                                                      \
          *__b++ = __tmp;                                                     \
        } while (--__size > 0);                                               \
    } while (0)

/* Discontinue quicksort algorithm when partition gets below this size.
   This particular magic number was chosen to work best on a Sun 4/260. */
#define MAX_THRESH 4

/* Stack node declarations used to store unfulfilled partition obligations. */
typedef struct
{
  char *lo;
  char *hi;
}
stack_node;

/* The next 4 #defines implement a very fast in-line stack abstraction. */
#define STACK_SIZE      (8 * sizeof(unsigned long int))
#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
#define POP(low, high)  ((void) (--top, (low = top->lo), (high = top->hi)))
#define STACK_NOT_EMPTY (stack < top)


/* Order size using quicksort.  This implementation incorporates
 * four optimizations discussed in Sedgewick:
 *
 * 1. Non-recursive, using an explicit stack of pointer that store the next
 *    array partition to sort.  To save time, this maximum amount of space
 *    required to store an array of MAX_INT is allocated on the stack.  Assuming
 *    a 32-bit integer, this needs only 32 * sizeof(stack_node) == 136 bits.
 *    Pretty cheap, actually.
 *
 * 2. Chose the pivot element using a median-of-three decision tree.  This
 *    reduces the probability of selecting a bad pivot value and eliminates
 *    certain * extraneous comparisons.
 *
 * 3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving insertion
 *    sort to order the MAX_THRESH items within each partition.  This is a big
 *    win, since insertion sort is faster for small, mostly sorted array
 *    segments.
 *
 * 4. The larger of the two sub-partitions is always pushed onto the stack
 *    first, with the algorithm then concentrating on the smaller partition.
 *    This *guarantees* no more than log (n) stack size is needed (actually O(1)
 *    in this case)!
 */

/**
 * g_qsort_with_data:
 * @pbase: start of array to sort
 * @total_elems: elements in the array
 * @size: size of each element
 * @compare_func: function to compare elements
 * @user_data: data to pass to @compare_func
 *
 * This is just like the standard C qsort() function, but
 * the comparison routine accepts a user data argument.
 * 
 **/
void
g_qsort_with_data (gconstpointer    pbase,
                   gint             total_elems,
                   gsize            size,
                   GCompareDataFunc compare_func,
                   gpointer         user_data)
{
  register char *base_ptr = (char *) pbase;

  /* Allocating SIZE bytes for a pivot buffer facilitates a better
   * algorithm below since we can do comparisons directly on the pivot.
   */
  char *pivot_buffer = (char *) g_alloca (size);
  const size_t max_thresh = MAX_THRESH * size;

  g_return_if_fail (total_elems >= 0);
  g_return_if_fail (pbase != NULL || total_elems == 0);
  g_return_if_fail (compare_func != NULL);

  if (total_elems == 0)
    return;

  if (total_elems > MAX_THRESH)
    {
      char *lo = base_ptr;
      char *hi = &lo[size * (total_elems - 1)];
      /* Largest size needed for 32-bit int!!! */
      stack_node stack[STACK_SIZE];
      stack_node *top = stack + 1;

      while (STACK_NOT_EMPTY)
        {
          char *left_ptr;
          char *right_ptr;

          char *pivot = pivot_buffer;

          /* Select median value from among LO, MID, and HI. Rearrange
           * LO and HI so the three values are sorted. This lowers the
           * probability of picking a pathological pivot value and
           * skips a comparison for both the LEFT_PTR and RIGHT_PTR. */

          char *mid = lo + size * ((hi - lo) / size >> 1);

          if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
            SWAP (mid, lo, size);
          if ((*compare_func) ((void *) hi, (void *) mid, user_data) < 0)
            SWAP (mid, hi, size);
          else
            goto jump_over;
          if ((*compare_func) ((void *) mid, (void *) lo, user_data) < 0)
            SWAP (mid, lo, size);
        jump_over:;
          memcpy (pivot, mid, size);
          pivot = pivot_buffer;

          left_ptr = lo + size;
          right_ptr = hi - size;

          /* Here's the famous ``collapse the walls'' section of quicksort.
           * Gotta like those tight inner loops!  They are the main reason
           * that this algorithm runs much faster than others. */
          do
            {
              while ((*compare_func)
                     ((void *) left_ptr, (void *) pivot,
                      user_data) < 0)
                left_ptr += size;

              while ((*compare_func)
                     ((void *) pivot, (void *) right_ptr,
                      user_data) < 0)
                right_ptr -= size;

              if (left_ptr < right_ptr)
                {
                  SWAP (left_ptr, right_ptr, size);
                  left_ptr += size;
                  right_ptr -= size;
                }
              else if (left_ptr == right_ptr)
                {
                  left_ptr += size;
                  right_ptr -= size;
                  break;
                }
            }
          while (left_ptr <= right_ptr);

          /* Set up pointers for next iteration.  First determine whether
           * left and right partitions are below the threshold size.  If so,
           * ignore one or both.  Otherwise, push the larger partition's
           * bounds on the stack and continue sorting the smaller one. */

          if ((size_t) (right_ptr - lo) <= max_thresh)
            {
              if ((size_t) (hi - left_ptr) <= max_thresh)
                /* Ignore both small partitions. */
                POP (lo, hi);
              else
                /* Ignore small left partition. */
                lo = left_ptr;
            }
          else if ((size_t) (hi - left_ptr) <= max_thresh)
                                /* Ignore small right partition. */
            hi = right_ptr;
          else if ((right_ptr - lo) > (hi - left_ptr))
            {
                                /* Push larger left partition indices. */
              PUSH (lo, right_ptr);
              lo = left_ptr;

            }
          else
            {
                                /* Push larger right partition indices. */
              PUSH (left_ptr, hi);
              hi = right_ptr;
            }
        }
    }

  /* Once the BASE_PTR array is partially sorted by quicksort the rest
   * is completely sorted using insertion sort, since this is efficient
   * for partitions below MAX_THRESH size. BASE_PTR points to the beginning
   * of the array to sort, and END_PTR points at the very last element in
   * the array (*not* one beyond it!). */

  {
    char *const end_ptr = &base_ptr[size * (total_elems - 1)];
    char *tmp_ptr = base_ptr;
    char *thresh = MIN (end_ptr, base_ptr + max_thresh);
    register char *run_ptr;

    /* Find smallest element in first threshold and place it at the
     * array's beginning.  This is the smallest array element,
     * and the operation speeds up insertion sort's inner loop. */

    for (run_ptr = tmp_ptr + size; run_ptr <= thresh;
         run_ptr +=
           size) if ((*compare_func) ((void *) run_ptr, (void *) tmp_ptr,
                                      user_data) < 0)
             tmp_ptr = run_ptr;

    if (tmp_ptr != base_ptr)
      SWAP (tmp_ptr, base_ptr, size);

    /* Insertion sort, running from left-hand-side up to right-hand-side.  */

    run_ptr = base_ptr + size;
    while ((run_ptr += size) <= end_ptr)
      {
        tmp_ptr = run_ptr - size;
        while ((*compare_func)
               ((void *) run_ptr, (void *) tmp_ptr,
                user_data) < 0)
          tmp_ptr -= size;

        tmp_ptr += size;
        if (tmp_ptr != run_ptr)
          {
            char *trav;

            trav = run_ptr + size;
            while (--trav >= run_ptr)
              {
                char c = *trav;
                char *hi, *lo;

                for (hi = lo = trav;
                     (lo -= size) >= tmp_ptr; hi = lo)
                  *hi = *lo;
                *hi = c;
              }
          }
      }
  }
}