315 lines
12 KiB
C
315 lines
12 KiB
C
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/*
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* This file is a part of Pcompress, a chunked parallel multi-
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* algorithm lossless compression and decompression program.
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*
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* Copyright (C) 2012-2013 Moinak Ghosh. All rights reserved.
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* Use is subject to license terms.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 3 of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this program.
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* If not, see <http://www.gnu.org/licenses/>.
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*
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* moinakg@belenix.org, http://moinakg.wordpress.com/
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*/
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/* $Id: qsort.h,v 1.5 2008-01-28 18:16:49 mjt Exp $
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* Adopted from GNU glibc by Mjt.
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* See stdlib/qsort.c in glibc */
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/* Copyright (C) 1991, 1992, 1996, 1997, 1999 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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/* in-line qsort implementation. Differs from traditional qsort() routine
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* in that it is a macro, not a function, and instead of passing an address
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* of a comparison routine to the function, it is possible to inline
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* comparison routine, thus speeding up sorting a lot.
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*
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* Usage:
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* #include "iqsort.h"
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* #define islt(a,b) (strcmp((*a),(*b))<0)
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* char *arr[];
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* int n;
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* QSORT(char*, arr, n, islt);
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*
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* The "prototype" and 4 arguments are:
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* QSORT(TYPE,BASE,NELT,ISLT)
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* 1) type of each element, TYPE,
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* 2) address of the beginning of the array, of type TYPE*,
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* 3) number of elements in the array, and
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* 4) comparision routine.
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* Array pointer and number of elements are referenced only once.
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* This is similar to a call
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* qsort(BASE,NELT,sizeof(TYPE),ISLT)
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* with the difference in last parameter.
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* Note the islt macro/routine (it receives pointers to two elements):
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* the only condition of interest is whenever one element is less than
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* another, no other conditions (greather than, equal to etc) are tested.
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* So, for example, to define integer sort, use:
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* #define islt(a,b) ((*a)<(*b))
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* QSORT(int, arr, n, islt)
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*
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* The macro could be used to implement a sorting function (see examples
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* below), or to implement the sorting algorithm inline. That is, either
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* create a sorting function and use it whenever you want to sort something,
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* or use QSORT() macro directly instead a call to such routine. Note that
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* the macro expands to quite some code (compiled size of int qsort on x86
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* is about 700..800 bytes).
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*
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* Using this macro directly it isn't possible to implement traditional
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* qsort() routine, because the macro assumes sizeof(element) == sizeof(TYPE),
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* while qsort() allows element size to be different.
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*
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* Several ready-to-use examples:
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*
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* Sorting array of integers:
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* void int_qsort(int *arr, unsigned n) {
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* #define int_lt(a,b) ((*a)<(*b))
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* QSORT(int, arr, n, int_lt);
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* }
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*
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* Sorting array of string pointers:
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* void str_qsort(char *arr[], unsigned n) {
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* #define str_lt(a,b) (strcmp((*a),(*b)) < 0)
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* QSORT(char*, arr, n, str_lt);
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* }
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*
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* Sorting array of structures:
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*
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* struct elt {
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* int key;
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* ...
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* };
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* void elt_qsort(struct elt *arr, unsigned n) {
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* #define elt_lt(a,b) ((a)->key < (b)->key)
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* QSORT(struct elt, arr, n, elt_lt);
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* }
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*
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* And so on.
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*/
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/* Swap two items pointed to by A and B using temporary buffer t. */
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#define _QSORT_SWAP(a, b, t) ((void)((t = *a), (*a = *b), (*b = t)))
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/* Discontinue quicksort algorithm when partition gets below this size.
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This particular magic number was chosen to work best on a Sun 4/260. */
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#define _QSORT_MAX_THRESH 4
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/* Stack node declarations used to store unfulfilled partition obligations
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* (inlined in QSORT).
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typedef struct {
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QSORT_TYPE *_lo, *_hi;
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} qsort_stack_node;
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*/
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/* The next 4 #defines implement a very fast in-line stack abstraction. */
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/* The stack needs log (total_elements) entries (we could even subtract
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log(MAX_THRESH)). Since total_elements has type unsigned, we get as
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upper bound for log (total_elements):
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bits per byte (CHAR_BIT) * sizeof(unsigned). */
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#define _QSORT_STACK_SIZE (8 * sizeof(unsigned))
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#define _QSORT_PUSH(top, low, high) \
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(((top->_lo = (low)), (top->_hi = (high)), ++top))
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#define _QSORT_POP(low, high, top) \
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((--top, (low = top->_lo), (high = top->_hi)))
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#define _QSORT_STACK_NOT_EMPTY (_stack < _top)
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/* Order size using quicksort. This implementation incorporates
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four optimizations discussed in Sedgewick:
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1. Non-recursive, using an explicit stack of pointer that store the
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next array partition to sort. To save time, this maximum amount
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of space required to store an array of SIZE_MAX is allocated on the
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stack. Assuming a 32-bit (64 bit) integer for size_t, this needs
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only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
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Pretty cheap, actually.
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2. Chose the pivot element using a median-of-three decision tree.
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This reduces the probability of selecting a bad pivot value and
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eliminates certain extraneous comparisons.
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3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
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insertion sort to order the MAX_THRESH items within each partition.
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This is a big win, since insertion sort is faster for small, mostly
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sorted array segments.
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4. The larger of the two sub-partitions is always pushed onto the
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stack first, with the algorithm then concentrating on the
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smaller partition. This *guarantees* no more than log (total_elems)
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stack size is needed (actually O(1) in this case)! */
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/* The main code starts here... */
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#define QSORT(QSORT_BASE,QSORT_NELT) \
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{ \
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QSORT_TYPE *const _base = (QSORT_BASE); \
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const unsigned _elems = (QSORT_NELT); \
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QSORT_TYPE _hold; \
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\
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/* Don't declare two variables of type QSORT_TYPE in a single \
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* statement: eg `TYPE a, b;', in case if TYPE is a pointer, \
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* expands to `type* a, b;' wich isn't what we want. \
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*/ \
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\
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if (_elems > _QSORT_MAX_THRESH) { \
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QSORT_TYPE *_lo = _base; \
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QSORT_TYPE *_hi = _lo + _elems - 1; \
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struct { \
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QSORT_TYPE *_hi; QSORT_TYPE *_lo; \
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} _stack[_QSORT_STACK_SIZE], *_top = _stack + 1; \
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\
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while (_QSORT_STACK_NOT_EMPTY) { \
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QSORT_TYPE *_left_ptr; QSORT_TYPE *_right_ptr; \
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\
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/* Select median value from among LO, MID, and HI. Rearrange \
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LO and HI so the three values are sorted. This lowers the \
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probability of picking a pathological pivot value and \
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skips a comparison for both the LEFT_PTR and RIGHT_PTR in \
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the while loops. */ \
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\
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QSORT_TYPE *_mid = _lo + ((_hi - _lo) >> 1); \
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\
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if (QSORT_LT (_mid, _lo)) \
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_QSORT_SWAP (_mid, _lo, _hold); \
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if (QSORT_LT (_hi, _mid)) { \
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_QSORT_SWAP (_mid, _hi, _hold); \
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if (QSORT_LT (_mid, _lo)) \
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_QSORT_SWAP (_mid, _lo, _hold); \
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} \
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\
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_left_ptr = _lo + 1; \
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_right_ptr = _hi - 1; \
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\
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/* Here's the famous ``collapse the walls'' section of quicksort. \
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Gotta like those tight inner loops! They are the main reason \
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that this algorithm runs much faster than others. */ \
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do { \
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while (QSORT_LT (_left_ptr, _mid)) \
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++_left_ptr; \
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\
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while (QSORT_LT (_mid, _right_ptr)) \
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--_right_ptr; \
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\
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if (_left_ptr < _right_ptr) { \
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_QSORT_SWAP (_left_ptr, _right_ptr, _hold); \
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if (_mid == _left_ptr) \
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_mid = _right_ptr; \
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else if (_mid == _right_ptr) \
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_mid = _left_ptr; \
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++_left_ptr; \
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--_right_ptr; \
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} \
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else if (_left_ptr == _right_ptr) { \
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++_left_ptr; \
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--_right_ptr; \
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break; \
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} \
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} while (_left_ptr <= _right_ptr); \
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\
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/* Set up pointers for next iteration. First determine whether \
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left and right partitions are below the threshold size. If so, \
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ignore one or both. Otherwise, push the larger partition's \
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bounds on the stack and continue sorting the smaller one. */ \
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\
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if (_right_ptr - _lo <= _QSORT_MAX_THRESH) { \
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if (_hi - _left_ptr <= _QSORT_MAX_THRESH) \
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/* Ignore both small partitions. */ \
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_QSORT_POP (_lo, _hi, _top); \
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else \
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/* Ignore small left partition. */ \
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_lo = _left_ptr; \
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} \
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else if (_hi - _left_ptr <= _QSORT_MAX_THRESH) \
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/* Ignore small right partition. */ \
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_hi = _right_ptr; \
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else if (_right_ptr - _lo > _hi - _left_ptr) { \
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/* Push larger left partition indices. */ \
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_QSORT_PUSH (_top, _lo, _right_ptr); \
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_lo = _left_ptr; \
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} \
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else { \
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/* Push larger right partition indices. */ \
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_QSORT_PUSH (_top, _left_ptr, _hi); \
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_hi = _right_ptr; \
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} \
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} \
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} \
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\
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/* Once the BASE array is partially sorted by quicksort the rest \
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is completely sorted using insertion sort, since this is efficient \
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for partitions below MAX_THRESH size. BASE points to the \
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beginning of the array to sort, and END_PTR points at the very \
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last element in the array (*not* one beyond it!). */ \
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\
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{ \
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QSORT_TYPE *const _end_ptr = _base + _elems - 1; \
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QSORT_TYPE *_tmp_ptr = _base; \
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register QSORT_TYPE *_run_ptr; \
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QSORT_TYPE *_thresh; \
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\
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_thresh = _base + _QSORT_MAX_THRESH; \
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if (_thresh > _end_ptr) \
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_thresh = _end_ptr; \
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\
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/* Find smallest element in first threshold and place it at the \
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array's beginning. This is the smallest array element, \
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and the operation speeds up insertion sort's inner loop. */ \
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\
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for (_run_ptr = _tmp_ptr + 1; _run_ptr <= _thresh; ++_run_ptr) \
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if (QSORT_LT (_run_ptr, _tmp_ptr)) \
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_tmp_ptr = _run_ptr; \
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\
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if (_tmp_ptr != _base) \
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_QSORT_SWAP (_tmp_ptr, _base, _hold); \
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\
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/* Insertion sort, running from left-hand-side \
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* up to right-hand-side. */ \
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\
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_run_ptr = _base + 1; \
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while (++_run_ptr <= _end_ptr) { \
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_tmp_ptr = _run_ptr - 1; \
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while (QSORT_LT (_run_ptr, _tmp_ptr)) \
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--_tmp_ptr; \
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\
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++_tmp_ptr; \
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if (_tmp_ptr != _run_ptr) { \
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QSORT_TYPE *_trav = _run_ptr + 1; \
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while (--_trav >= _run_ptr) { \
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QSORT_TYPE *_hi; QSORT_TYPE *_lo; \
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_hold = *_trav; \
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\
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for (_hi = _lo = _trav; --_lo >= _tmp_ptr; _hi = _lo) \
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*_hi = *_lo; \
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*_hi = _hold; \
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} \
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} \
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} \
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} \
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\
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}
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