The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/libsa/sort.c

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    1 /*
    2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
    3  *
    4  * @APPLE_LICENSE_HEADER_START@
    5  * 
    6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
    7  * 
    8  * This file contains Original Code and/or Modifications of Original Code
    9  * as defined in and that are subject to the Apple Public Source License
   10  * Version 2.0 (the 'License'). You may not use this file except in
   11  * compliance with the License. Please obtain a copy of the License at
   12  * http://www.opensource.apple.com/apsl/ and read it before using this
   13  * file.
   14  * 
   15  * The Original Code and all software distributed under the License are
   16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
   17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
   18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
   19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
   20  * Please see the License for the specific language governing rights and
   21  * limitations under the License.
   22  * 
   23  * @APPLE_LICENSE_HEADER_END@
   24  */
   25 /*-
   26  * Copyright (c) 1991, 1993
   27  *      The Regents of the University of California.  All rights reserved.
   28  *
   29  * This code is derived from software contributed to Berkeley by
   30  * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
   31  *
   32  * Redistribution and use in source and binary forms, with or without
   33  * modification, are permitted provided that the following conditions
   34  * are met:
   35  * 1. Redistributions of source code must retain the above copyright
   36  *    notice, this list of conditions and the following disclaimer.
   37  * 2. Redistributions in binary form must reproduce the above copyright
   38  *    notice, this list of conditions and the following disclaimer in the
   39  *    documentation and/or other materials provided with the distribution.
   40  * 3. All advertising materials mentioning features or use of this software
   41  *    must display the following acknowledgement:
   42  *      This product includes software developed by the University of
   43  *      California, Berkeley and its contributors.
   44  * 4. Neither the name of the University nor the names of its contributors
   45  *    may be used to endorse or promote products derived from this software
   46  *    without specific prior written permission.
   47  *
   48  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   58  * SUCH DAMAGE.
   59  */
   60 
   61 #if defined(LIBC_SCCS) && !defined(lint)
   62 static char sccsid[] = "@(#)heapsort.c  8.1 (Berkeley) 6/4/93";
   63 #endif /* LIBC_SCCS and not lint */
   64 
   65 
   66 #include <libsa/stdlib.h>
   67 
   68 
   69 /*
   70  * Swap two areas of size number of bytes.  Although qsort(3) permits random
   71  * blocks of memory to be sorted, sorting pointers is almost certainly the
   72  * common case (and, were it not, could easily be made so).  Regardless, it
   73  * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
   74  * arithmetic gets lost in the time required for comparison function calls.
   75  */
   76 #define SWAP(a, b, count, size, tmp) { \
   77         count = size; \
   78         do { \
   79                 tmp = *a; \
   80                 *a++ = *b; \
   81                 *b++ = tmp; \
   82         } while (--count); \
   83 }
   84 
   85 /* Copy one block of size size to another. */
   86 #define COPY(a, b, count, size, tmp1, tmp2) { \
   87         count = size; \
   88         tmp1 = a; \
   89         tmp2 = b; \
   90         do { \
   91                 *tmp1++ = *tmp2++; \
   92         } while (--count); \
   93 }
   94 
   95 /*
   96  * Build the list into a heap, where a heap is defined such that for
   97  * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
   98  *
   99  * There two cases.  If j == nmemb, select largest of Ki and Kj.  If
  100  * j < nmemb, select largest of Ki, Kj and Kj+1.
  101  */
  102 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
  103         for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
  104             par_i = child_i) { \
  105                 child = base + child_i * size; \
  106                 if (child_i < nmemb && compar(child, child + size) < 0) { \
  107                         child += size; \
  108                         ++child_i; \
  109                 } \
  110                 par = base + par_i * size; \
  111                 if (compar(child, par) <= 0) \
  112                         break; \
  113                 SWAP(par, child, count, size, tmp); \
  114         } \
  115 }
  116 
  117 /*
  118  * Select the top of the heap and 'heapify'.  Since by far the most expensive
  119  * action is the call to the compar function, a considerable optimization
  120  * in the average case can be achieved due to the fact that k, the displaced
  121  * elememt, is ususally quite small, so it would be preferable to first
  122  * heapify, always maintaining the invariant that the larger child is copied
  123  * over its parent's record.
  124  *
  125  * Then, starting from the *bottom* of the heap, finding k's correct place,
  126  * again maintianing the invariant.  As a result of the invariant no element
  127  * is 'lost' when k is assigned its correct place in the heap.
  128  *
  129  * The time savings from this optimization are on the order of 15-20% for the
  130  * average case. See Knuth, Vol. 3, page 158, problem 18.
  131  *
  132  * XXX Don't break the #define SELECT line, below.  Reiser cpp gets upset.
  133  */
  134 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
  135         for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
  136                 child = base + child_i * size; \
  137                 if (child_i < nmemb && compar(child, child + size) < 0) { \
  138                         child += size; \
  139                         ++child_i; \
  140                 } \
  141                 par = base + par_i * size; \
  142                 COPY(par, child, count, size, tmp1, tmp2); \
  143         } \
  144         for (;;) { \
  145                 child_i = par_i; \
  146                 par_i = child_i / 2; \
  147                 child = base + child_i * size; \
  148                 par = base + par_i * size; \
  149                 if (child_i == 1 || compar(k, par) < 0) { \
  150                         COPY(child, k, count, size, tmp1, tmp2); \
  151                         break; \
  152                 } \
  153                 COPY(child, par, count, size, tmp1, tmp2); \
  154         } \
  155 }
  156 
  157 /* Pass heapsort off as qsort for krld. -- Nik Gervae
  158  *
  159  * Heapsort -- Knuth, Vol. 3, page 145.  Runs in O (N lg N), both average
  160  * and worst.  While heapsort is faster than the worst case of quicksort,
  161  * the BSD quicksort does median selection so that the chance of finding
  162  * a data set that will trigger the worst case is nonexistent.  Heapsort's
  163  * only advantage over quicksort is that it requires little additional memory.
  164  */
  165 __private_extern__
  166 void qsort(void * vbase, size_t nmemb, size_t size,
  167         int (*compar)(const void *, const void *)) {
  168 
  169         register int cnt, i, j, l;
  170         register char tmp, *tmp1, *tmp2;
  171         char *base, *k, *p, *t;
  172 
  173         if (nmemb <= 1) {
  174             return;
  175         }
  176 
  177         if (!size) {
  178             return;
  179         }
  180 
  181         if ((k = (char *)malloc(size)) == NULL) {
  182 //            panic();
  183             return;
  184         }
  185 
  186         /*
  187          * Items are numbered from 1 to nmemb, so offset from size bytes
  188          * below the starting address.
  189          */
  190         base = (char *)vbase - size;
  191 
  192         for (l = nmemb / 2 + 1; --l;)
  193                 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
  194 
  195         /*
  196          * For each element of the heap, save the largest element into its
  197          * final slot, save the displaced element (k), then recreate the
  198          * heap.
  199          */
  200         while (nmemb > 1) {
  201                 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
  202                 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
  203                 --nmemb;
  204                 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
  205         }
  206         free(k);
  207         return;
  208 }

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