PandA-2024.02
qsort-specialized.c
Go to the documentation of this file.
1 /* Copyright (C) 1991-2014 Free Software Foundation, Inc.
2  This file is part of the GNU C Library.
3  Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
4 
5  The GNU C Library is free software; you can redistribute it and/or
6  modify it under the terms of the GNU Lesser General Public
7  License as published by the Free Software Foundation; either
8  version 2.1 of the License, or (at your option) any later version.
9 
10  The GNU C Library is distributed in the hope that it will be useful,
11  but WITHOUT ANY WARRANTY; without even the implied warranty of
12  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13  Lesser General Public License for more details.
14 
15  You should have received a copy of the GNU Lesser General Public
16  License along with the GNU C Library; if not, see
17  <http://www.gnu.org/licenses/>. */
18 
19 /* If you consider tuning this algorithm, you should consult first:
20  Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
21  Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */
22 
23 #include <limits.h>
24 #include <stdlib.h>
25 
26 /* Byte-wise swap two items of size SIZE. */
27 #define SWAP(a, b, size) \
28  do \
29  { \
30  size_t __size = (size); \
31  char *__a = (a), *__b = (b); \
32  do \
33  { \
34  char __tmp = *__a; \
35  *__a++ = *__b; \
36  *__b++ = __tmp; \
37  } while (--__size > 0); \
38  } while (0)
39 
40 /* Discontinue quicksort algorithm when partition gets below this size.
41  This particular magic number was chosen to work best on a Sun 4/260. */
42 #define MAX_THRESH 4
43 
44 /* Stack node declarations used to store unfulfilled partition obligations. */
45 typedef struct
46  {
47  char *lo;
48  char *hi;
49  } stack_node;
50 
51 /* The next 4 #defines implement a very fast in-line stack abstraction. */
52 /* The stack needs log (total_elements) entries (we could even subtract
53  log(MAX_THRESH)). Since total_elements has type size_t, we get as
54  upper bound for log (total_elements):
55  bits per byte (CHAR_BIT) * sizeof(size_t). */
56 #define STACK_SIZE (CHAR_BIT * sizeof(size_t))
57 #define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
58 #define POP(low, high) ((void) (--top, (low = top->lo), (high = top->hi)))
59 #define STACK_NOT_EMPTY (stack < top)
60 
61 int less (const void *, const void *, void *);
62 
63 /* Order size using quicksort. This implementation incorporates
64  four optimizations discussed in Sedgewick:
65 
66  1. Non-recursive, using an explicit stack of pointer that store the
67  next array partition to sort. To save time, this maximum amount
68  of space required to store an array of SIZE_MAX is allocated on the
69  stack. Assuming a 32-bit (64 bit) integer for size_t, this needs
70  only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
71  Pretty cheap, actually.
72 
73  2. Chose the pivot element using a median-of-three decision tree.
74  This reduces the probability of selecting a bad pivot value and
75  eliminates certain extraneous comparisons.
76 
77  3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
78  insertion sort to order the MAX_THRESH items within each partition.
79  This is a big win, since insertion sort is faster for small, mostly
80  sorted array segments.
81 
82  4. The larger of the two sub-partitions is always pushed onto the
83  stack first, with the algorithm then concentrating on the
84  smaller partition. This *guarantees* no more than log (total_elems)
85  stack size is needed (actually O(1) in this case)! */
86 
87 void
88 _quicksort (void *const pbase, size_t total_elems, size_t size,
89  int (*cmp)(const void *, const void *, void *), void *arg)
90 {
91  char *base_ptr = (char *) pbase;
92 
93  const size_t max_thresh = MAX_THRESH * size;
94 
95  if (total_elems == 0)
96  /* Avoid lossage with unsigned arithmetic below. */
97  return;
98 
99  if (total_elems > MAX_THRESH)
100  {
101  char *lo = base_ptr;
102  char *hi = &lo[size * (total_elems - 1)];
104  stack_node *top = stack;
105 
106  PUSH (NULL, NULL);
107 
108  while (STACK_NOT_EMPTY)
109  {
110  char *left_ptr;
111  char *right_ptr;
112 
113  /* Select median value from among LO, MID, and HI. Rearrange
114  LO and HI so the three values are sorted. This lowers the
115  probability of picking a pathological pivot value and
116  skips a comparison for both the LEFT_PTR and RIGHT_PTR in
117  the while loops. */
118 
119  char *mid = lo + size * ((hi - lo) / size >> 1);
120 
121  if (less ((void *) mid, (void *) lo, arg) < 0)
122  SWAP (mid, lo, size);
123  if (less ((void *) hi, (void *) mid, arg) < 0)
124  SWAP (mid, hi, size);
125  else
126  goto jump_over;
127  if (less ((void *) mid, (void *) lo, arg) < 0)
128  SWAP (mid, lo, size);
129  jump_over:;
130 
131  left_ptr = lo + size;
132  right_ptr = hi - size;
133 
134  /* Here's the famous ``collapse the walls'' section of quicksort.
135  Gotta like those tight inner loops! They are the main reason
136  that this algorithm runs much faster than others. */
137  do
138  {
139  while (less ((void *) left_ptr, (void *) mid, arg) < 0)
140  left_ptr += size;
141 
142  while (less ((void *) mid, (void *) right_ptr, arg) < 0)
143  right_ptr -= size;
144 
145  if (left_ptr < right_ptr)
146  {
147  SWAP (left_ptr, right_ptr, size);
148  if (mid == left_ptr)
149  mid = right_ptr;
150  else if (mid == right_ptr)
151  mid = left_ptr;
152  left_ptr += size;
153  right_ptr -= size;
154  }
155  else if (left_ptr == right_ptr)
156  {
157  left_ptr += size;
158  right_ptr -= size;
159  break;
160  }
161  }
162  while (left_ptr <= right_ptr);
163 
164  /* Set up pointers for next iteration. First determine whether
165  left and right partitions are below the threshold size. If so,
166  ignore one or both. Otherwise, push the larger partition's
167  bounds on the stack and continue sorting the smaller one. */
168 
169  if ((size_t) (right_ptr - lo) <= max_thresh)
170  {
171  if ((size_t) (hi - left_ptr) <= max_thresh)
172  /* Ignore both small partitions. */
173  POP (lo, hi);
174  else
175  /* Ignore small left partition. */
176  lo = left_ptr;
177  }
178  else if ((size_t) (hi - left_ptr) <= max_thresh)
179  /* Ignore small right partition. */
180  hi = right_ptr;
181  else if ((right_ptr - lo) > (hi - left_ptr))
182  {
183  /* Push larger left partition indices. */
184  PUSH (lo, right_ptr);
185  lo = left_ptr;
186  }
187  else
188  {
189  /* Push larger right partition indices. */
190  PUSH (left_ptr, hi);
191  hi = right_ptr;
192  }
193  }
194  }
195 
196  /* Once the BASE_PTR array is partially sorted by quicksort the rest
197  is completely sorted using insertion sort, since this is efficient
198  for partitions below MAX_THRESH size. BASE_PTR points to the beginning
199  of the array to sort, and END_PTR points at the very last element in
200  the array (*not* one beyond it!). */
201 
202 #define min(x, y) ((x) < (y) ? (x) : (y))
203 
204  {
205  char *const end_ptr = &base_ptr[size * (total_elems - 1)];
206  char *tmp_ptr = base_ptr;
207  char *thresh = min(end_ptr, base_ptr + max_thresh);
208  char *run_ptr;
209 
210  /* Find smallest element in first threshold and place it at the
211  array's beginning. This is the smallest array element,
212  and the operation speeds up insertion sort's inner loop. */
213 
214  for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
215  if (less ((void *) run_ptr, (void *) tmp_ptr, arg) < 0)
216  tmp_ptr = run_ptr;
217 
218  if (tmp_ptr != base_ptr)
219  SWAP (tmp_ptr, base_ptr, size);
220 
221  /* Insertion sort, running from left-hand-side up to right-hand-side. */
222 
223  run_ptr = base_ptr + size;
224  while ((run_ptr += size) <= end_ptr)
225  {
226  tmp_ptr = run_ptr - size;
227  while (less ((void *) run_ptr, (void *) tmp_ptr, arg) < 0)
228  tmp_ptr -= size;
229 
230  tmp_ptr += size;
231  if (tmp_ptr != run_ptr)
232  {
233  char *trav;
234 
235  trav = run_ptr + size;
236  while (--trav >= run_ptr)
237  {
238  char c = *trav;
239  char *hi, *lo;
240 
241  for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
242  *hi = *lo;
243  *hi = c;
244  }
245  }
246  }
247  }
248 }
#define NULL
#define min(x, y)
void * top(node_stack *head)
Definition: tree.c:75
#define PUSH(low, high)
#define STACK_NOT_EMPTY
void _quicksort(void *const pbase, size_t total_elems, size_t size, int(*cmp)(const void *, const void *, void *), void *arg)
#define MAX_THRESH
int less(const void *, const void *, void *)
Definition: less.c:4
#define STACK_SIZE
#define SWAP(a, b, size)
Definition: tree.c:10
#define POP(low, high)

Generated on Mon Feb 12 2024 13:02:49 for PandA-2024.02 by doxygen 1.8.13