1 /* Copyright (C) 1991,1992,1996,1997,1999,2004 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
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.
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.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */
18 /* If you consider tuning this algorithm, you should consult first:
19 Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
20 Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */
22 /* Modified to be used in samba4 by
23 * Simo Sorce <idra@samba.org> 2005
26 #include "ldb_private.h"
28 /* Byte-wise swap two items of size SIZE. */
29 #define SWAP(a, b, size) \
32 register size_t __size = (size); \
33 register char *__a = (a), *__b = (b); \
39 } while (--__size > 0); \
42 /* Discontinue quicksort algorithm when partition gets below this size.
43 This particular magic number was chosen to work best on a Sun 4/260. */
46 /* Stack node declarations used to store unfulfilled partition obligations. */
53 /* The next 4 #defines implement a very fast in-line stack abstraction. */
54 /* The stack needs log (total_elements) entries (we could even subtract
55 log(MAX_THRESH)). Since total_elements has type size_t, we get as
56 upper bound for log (total_elements):
57 bits per byte (CHAR_BIT) * sizeof(size_t). */
61 #define STACK_SIZE (CHAR_BIT * sizeof(size_t))
62 #define PUSH(low, high) ((void) ((stack[i].lo = (low)), (stack[i].hi = (high)), i++))
63 #define POP(low, high) ((void) (i--, (low = stack[i].lo), (high = stack[i].hi)))
66 /* Order size using quicksort. This implementation incorporates
67 four optimizations discussed in Sedgewick:
69 1. Non-recursive, using an explicit stack of pointer that store the
70 next array partition to sort. To save time, this maximum amount
71 of space required to store an array of SIZE_MAX is allocated on the
72 stack. Assuming a 32-bit (64 bit) integer for size_t, this needs
73 only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
74 Pretty cheap, actually.
76 2. Chose the pivot element using a median-of-three decision tree.
77 This reduces the probability of selecting a bad pivot value and
78 eliminates certain extraneous comparisons.
80 3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
81 insertion sort to order the MAX_THRESH items within each partition.
82 This is a big win, since insertion sort is faster for small, mostly
83 sorted array segments.
85 4. The larger of the two sub-partitions is always pushed onto the
86 stack first, with the algorithm then concentrating on the
87 smaller partition. This *guarantees* no more than log (total_elems)
88 stack size is needed (actually O(1) in this case)! */
90 void ldb_qsort (void *const pbase
, size_t total_elems
, size_t size
,
91 void *opaque
, ldb_qsort_cmp_fn_t cmp
)
93 register char *base_ptr
= (char *) pbase
;
95 const size_t max_thresh
= MAX_THRESH
* size
;
98 /* Avoid lossage with unsigned arithmetic below. */
101 if (total_elems
> MAX_THRESH
)
104 char *hi
= &lo
[size
* (total_elems
- 1)];
105 stack_node stack
[STACK_SIZE
];
115 /* Select median value from among LO, MID, and HI. Rearrange
116 LO and HI so the three values are sorted. This lowers the
117 probability of picking a pathological pivot value and
118 skips a comparison for both the LEFT_PTR and RIGHT_PTR in
121 char *mid
= lo
+ size
* ((hi
- lo
) / size
>> 1);
123 if ((*cmp
) ((void *) mid
, (void *) lo
, opaque
) < 0)
124 SWAP (mid
, lo
, size
);
125 if ((*cmp
) ((void *) hi
, (void *) mid
, opaque
) < 0)
126 SWAP (mid
, hi
, size
);
129 if ((*cmp
) ((void *) mid
, (void *) lo
, opaque
) < 0)
130 SWAP (mid
, lo
, size
);
133 left_ptr
= lo
+ size
;
134 right_ptr
= hi
- size
;
136 /* Here's the famous ``collapse the walls'' section of quicksort.
137 Gotta like those tight inner loops! They are the main reason
138 that this algorithm runs much faster than others. */
141 while ((*cmp
) ((void *) left_ptr
, (void *) mid
, opaque
) < 0)
144 while ((*cmp
) ((void *) mid
, (void *) right_ptr
, opaque
) < 0)
147 if (left_ptr
< right_ptr
)
149 SWAP (left_ptr
, right_ptr
, size
);
152 else if (mid
== right_ptr
)
157 else if (left_ptr
== right_ptr
)
164 while (left_ptr
<= right_ptr
);
166 /* Set up pointers for next iteration. First determine whether
167 left and right partitions are below the threshold size. If so,
168 ignore one or both. Otherwise, push the larger partition's
169 bounds on the stack and continue sorting the smaller one. */
171 if ((size_t) (right_ptr
- lo
) <= max_thresh
)
173 if ((size_t) (hi
- left_ptr
) <= max_thresh
)
174 /* Ignore both small partitions. */
177 /* Ignore small left partition. */
180 else if ((size_t) (hi
- left_ptr
) <= max_thresh
)
181 /* Ignore small right partition. */
183 else if ((right_ptr
- lo
) > (hi
- left_ptr
))
185 /* Push larger left partition indices. */
186 PUSH (lo
, right_ptr
);
191 /* Push larger right partition indices. */
196 while (i
> 0 && i
< STACK_SIZE
);
199 /* Once the BASE_PTR array is partially sorted by quicksort the rest
200 is completely sorted using insertion sort, since this is efficient
201 for partitions below MAX_THRESH size. BASE_PTR points to the beginning
202 of the array to sort, and END_PTR points at the very last element in
203 the array (*not* one beyond it!). */
205 #define min(x, y) ((x) < (y) ? (x) : (y))
208 char *const end_ptr
= &base_ptr
[size
* (total_elems
- 1)];
209 char *tmp_ptr
= base_ptr
;
210 char *thresh
= min(end_ptr
, base_ptr
+ max_thresh
);
211 register char *run_ptr
;
213 /* Find smallest element in first threshold and place it at the
214 array's beginning. This is the smallest array element,
215 and the operation speeds up insertion sort's inner loop. */
217 for (run_ptr
= tmp_ptr
+ size
; run_ptr
<= thresh
; run_ptr
+= size
)
218 if ((*cmp
) ((void *) run_ptr
, (void *) tmp_ptr
, opaque
) < 0)
221 if (tmp_ptr
!= base_ptr
)
222 SWAP (tmp_ptr
, base_ptr
, size
);
224 /* Insertion sort, running from left-hand-side up to right-hand-side. */
226 run_ptr
= base_ptr
+ size
;
227 while ((run_ptr
+= size
) <= end_ptr
)
229 tmp_ptr
= run_ptr
- size
;
230 while ((*cmp
) ((void *) run_ptr
, (void *) tmp_ptr
, opaque
) < 0)
234 if (tmp_ptr
!= run_ptr
)
238 trav
= run_ptr
+ size
;
239 while (--trav
>= run_ptr
)
244 for (hi
= lo
= trav
; (lo
-= size
) >= tmp_ptr
; hi
= lo
)