diff options
Diffstat (limited to 'source4/lib')
| -rw-r--r-- | source4/lib/ldb/common/qsort.c | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/source4/lib/ldb/common/qsort.c b/source4/lib/ldb/common/qsort.c new file mode 100644 index 0000000000..2bb8890358 --- /dev/null +++ b/source4/lib/ldb/common/qsort.c @@ -0,0 +1,256 @@ +/* Copyright (C) 1991,1992,1996,1997,1999,2004 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Written by Douglas C. Schmidt (schmidt@ics.uci.edu). + + The GNU C 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 2.1 of the License, or (at your option) any later version. + + The GNU C 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 the GNU C Library; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +/* If you consider tuning this algorithm, you should consult first: + Engineering a sort function; Jon Bentley and M. Douglas McIlroy; + Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */ + +/* Modified to be used in samba4 by + * Simo Sorce <idra@samba.org> 2005 + */ + +#include "includes.h" +#include "ldb/include/ldb.h" + +#include <alloca.h> +#include <limits.h> +#include <stdlib.h> +#include <string.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. */ +/* The stack needs log (total_elements) entries (we could even subtract + log(MAX_THRESH)). Since total_elements has type size_t, we get as + upper bound for log (total_elements): + bits per byte (CHAR_BIT) * sizeof(size_t). */ +#define STACK_SIZE (CHAR_BIT * sizeof(size_t)) +#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 SIZE_MAX is allocated on the + stack. Assuming a 32-bit (64 bit) integer for size_t, this needs + only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes). + 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 (total_elems) + stack size is needed (actually O(1) in this case)! */ + +void ldb_qsort (void *const pbase, size_t total_elems, size_t size, + void *opaque, ldb_qsort_cmp_fn_t cmp) +{ + register char *base_ptr = (char *) pbase; + + const size_t max_thresh = MAX_THRESH * size; + + if (total_elems == 0) + /* Avoid lossage with unsigned arithmetic below. */ + return; + + if (total_elems > MAX_THRESH) + { + char *lo = base_ptr; + char *hi = &lo[size * (total_elems - 1)]; + stack_node stack[STACK_SIZE]; + stack_node *top = stack; + + PUSH (NULL, NULL); + + while (STACK_NOT_EMPTY) + { + char *left_ptr; + char *right_ptr; + + /* 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 in + the while loops. */ + + char *mid = lo + size * ((hi - lo) / size >> 1); + + if ((*cmp) ((void *) mid, (void *) lo, opaque) < 0) + SWAP (mid, lo, size); + if ((*cmp) ((void *) hi, (void *) mid, opaque) < 0) + SWAP (mid, hi, size); + else + goto jump_over; + if ((*cmp) ((void *) mid, (void *) lo, opaque) < 0) + SWAP (mid, lo, size); + jump_over:; + + 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 ((*cmp) ((void *) left_ptr, (void *) mid, opaque) < 0) + left_ptr += size; + + while ((*cmp) ((void *) mid, (void *) right_ptr, opaque) < 0) + right_ptr -= size; + + if (left_ptr < right_ptr) + { + SWAP (left_ptr, right_ptr, size); + if (mid == left_ptr) + mid = right_ptr; + else if (mid == right_ptr) + mid = left_ptr; + 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!). */ + +#define min(x, y) ((x) < (y) ? (x) : (y)) + + { + 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 ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, opaque) < 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 ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, opaque) < 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; + } + } + } + } +} |