+++ /dev/null
-/* Copyright (C) 1991, 1992 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 Library General Public License as
- published by the Free Software Foundation; either version 2 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
- Library General Public License for more details.
-
- You should have received a copy of the GNU Library General Public
- License along with the GNU C Library; see the file COPYING.LIB. If
- not, write to the Free Software Foundation, Inc., 675 Mass Ave,
- Cambridge, MA 02139, USA. */
-
-#include <config.h>
-#include <stdlib.h>
-#include <string.h>
-#include "alloc.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 segements.
-
- 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)! */
-
-void
-quicksort (void *pbase, size_t total_elems, size_t size,
- int (*cmp) (const void *, const void *, void *),
- void *param)
-{
- 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 = xmalloc (size);
- const size_t max_thresh = MAX_THRESH * size;
-
- if (total_elems == 0)
- {
- /* Avoid lossage with unsigned arithmetic below. */
- free (pivot_buffer);
- 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 ((*cmp) ((void *) mid, (void *) lo, param) < 0)
- SWAP (mid, lo, size);
- if ((*cmp) ((void *) hi, (void *) mid, param) < 0)
- SWAP (mid, hi, size);
- else
- goto jump_over;
- if ((*cmp) ((void *) mid, (void *) lo, param) < 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 ((*cmp) ((void *) left_ptr, (void *) pivot, param) < 0)
- left_ptr += size;
-
- while ((*cmp) ((void *) pivot, (void *) right_ptr, param) < 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!). */
-
-#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, param) < 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, param) < 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;
- }
- }
- }
- }
-
- free (pivot_buffer);
-}
projects / pspp-builds.git / commitdiff