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). 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 <http://www.gnu.org/licenses/>. */ 17 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. */ 21 22/* Modified to be used in samba4 by 23 * Simo Sorce <idra@samba.org> 2005 24 */ 25 26#include "ldb_private.h" 27 28/* Byte-wise swap two items of size SIZE. */ 29#define SWAP(a, b, size) \ 30 do \ 31 { \ 32 register size_t __size = (size); \ 33 register char *__a = (a), *__b = (b); \ 34 do \ 35 { \ 36 char __tmp = *__a; \ 37 *__a++ = *__b; \ 38 *__b++ = __tmp; \ 39 } while (--__size > 0); \ 40 } while (0) 41 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. */ 44#define MAX_THRESH 4 45 46/* Stack node declarations used to store unfulfilled partition obligations. */ 47typedef struct 48 { 49 char *lo; 50 char *hi; 51 } stack_node; 52 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). */ 58#ifndef CHAR_BIT 59#define CHAR_BIT 8 60#endif 61#define STACK_SIZE (CHAR_BIT * sizeof(size_t)) 62#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top)) 63#define POP(low, high) ((void) (--top, (low = top->lo), (high = top->hi))) 64#define STACK_NOT_EMPTY (stack < top) 65 66 67/* Order size using quicksort. This implementation incorporates 68 four optimizations discussed in Sedgewick: 69 70 1. Non-recursive, using an explicit stack of pointer that store the 71 next array partition to sort. To save time, this maximum amount 72 of space required to store an array of SIZE_MAX is allocated on the 73 stack. Assuming a 32-bit (64 bit) integer for size_t, this needs 74 only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes). 75 Pretty cheap, actually. 76 77 2. Chose the pivot element using a median-of-three decision tree. 78 This reduces the probability of selecting a bad pivot value and 79 eliminates certain extraneous comparisons. 80 81 3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving 82 insertion sort to order the MAX_THRESH items within each partition. 83 This is a big win, since insertion sort is faster for small, mostly 84 sorted array segments. 85 86 4. The larger of the two sub-partitions is always pushed onto the 87 stack first, with the algorithm then concentrating on the 88 smaller partition. This *guarantees* no more than log (total_elems) 89 stack size is needed (actually O(1) in this case)! */ 90 91void ldb_qsort (void *const pbase, size_t total_elems, size_t size, 92 void *opaque, ldb_qsort_cmp_fn_t cmp) 93{ 94 register char *base_ptr = (char *) pbase; 95 96 const size_t max_thresh = MAX_THRESH * size; 97 98 if (total_elems == 0) 99 /* Avoid lossage with unsigned arithmetic below. */ 100 return; 101 102 if (total_elems > MAX_THRESH) 103 { 104 char *lo = base_ptr; 105 char *hi = &lo[size * (total_elems - 1)]; 106 stack_node stack[STACK_SIZE]; 107 stack_node *top = stack; 108 109 PUSH (NULL, NULL); 110 111 while (STACK_NOT_EMPTY) 112 { 113 char *left_ptr; 114 char *right_ptr; 115 116 /* Select median value from among LO, MID, and HI. Rearrange 117 LO and HI so the three values are sorted. This lowers the 118 probability of picking a pathological pivot value and 119 skips a comparison for both the LEFT_PTR and RIGHT_PTR in 120 the while loops. */ 121 122 char *mid = lo + size * ((hi - lo) / size >> 1); 123 124 if ((*cmp) ((void *) mid, (void *) lo, opaque) < 0) 125 SWAP (mid, lo, size); 126 if ((*cmp) ((void *) hi, (void *) mid, opaque) < 0) 127 SWAP (mid, hi, size); 128 else 129 goto jump_over; 130 if ((*cmp) ((void *) mid, (void *) lo, opaque) < 0) 131 SWAP (mid, lo, size); 132 jump_over:; 133 134 left_ptr = lo + size; 135 right_ptr = hi - size; 136 137 /* Here's the famous ``collapse the walls'' section of quicksort. 138 Gotta like those tight inner loops! They are the main reason 139 that this algorithm runs much faster than others. */ 140 do 141 { 142 while ((*cmp) ((void *) left_ptr, (void *) mid, opaque) < 0) 143 left_ptr += size; 144 145 while ((*cmp) ((void *) mid, (void *) right_ptr, opaque) < 0) 146 right_ptr -= size; 147 148 if (left_ptr < right_ptr) 149 { 150 SWAP (left_ptr, right_ptr, size); 151 if (mid == left_ptr) 152 mid = right_ptr; 153 else if (mid == right_ptr) 154 mid = left_ptr; 155 left_ptr += size; 156 right_ptr -= size; 157 } 158 else if (left_ptr == right_ptr) 159 { 160 left_ptr += size; 161 right_ptr -= size; 162 break; 163 } 164 } 165 while (left_ptr <= right_ptr); 166 167 /* Set up pointers for next iteration. First determine whether 168 left and right partitions are below the threshold size. If so, 169 ignore one or both. Otherwise, push the larger partition's 170 bounds on the stack and continue sorting the smaller one. */ 171 172 if ((size_t) (right_ptr - lo) <= max_thresh) 173 { 174 if ((size_t) (hi - left_ptr) <= max_thresh) 175 /* Ignore both small partitions. */ 176 POP (lo, hi); 177 else 178 /* Ignore small left partition. */ 179 lo = left_ptr; 180 } 181 else if ((size_t) (hi - left_ptr) <= max_thresh) 182 /* Ignore small right partition. */ 183 hi = right_ptr; 184 else if ((right_ptr - lo) > (hi - left_ptr)) 185 { 186 /* Push larger left partition indices. */ 187 PUSH (lo, right_ptr); 188 lo = left_ptr; 189 } 190 else 191 { 192 /* Push larger right partition indices. */ 193 PUSH (left_ptr, hi); 194 hi = right_ptr; 195 } 196 } 197 } 198 199 /* 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!). */ 204 205#define min(x, y) ((x) < (y) ? (x) : (y)) 206 207 { 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; 212 213 /* 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. */ 216 217 for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size) 218 if ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, opaque) < 0) 219 tmp_ptr = run_ptr; 220 221 if (tmp_ptr != base_ptr) 222 SWAP (tmp_ptr, base_ptr, size); 223 224 /* Insertion sort, running from left-hand-side up to right-hand-side. */ 225 226 run_ptr = base_ptr + size; 227 while ((run_ptr += size) <= end_ptr) 228 { 229 tmp_ptr = run_ptr - size; 230 while ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, opaque) < 0) 231 tmp_ptr -= size; 232 233 tmp_ptr += size; 234 if (tmp_ptr != run_ptr) 235 { 236 char *trav; 237 238 trav = run_ptr + size; 239 while (--trav >= run_ptr) 240 { 241 char c = *trav; 242 char *hi, *lo; 243 244 for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo) 245 *hi = *lo; 246 *hi = c; 247 } 248 } 249 } 250 } 251} 252