The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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  * The contents of this file constitute Original Code as defined in and
    7  * are subject to the Apple Public Source License Version 1.1 (the
    8  * "License").  You may not use this file except in compliance with the
    9  * License.  Please obtain a copy of the License at
   10  * http://www.apple.com/publicsource and read it before using this file.
   11  * 
   12  * This Original Code and all software distributed under the License are
   13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
   14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
   15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
   16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
   17  * License for the specific language governing rights and limitations
   18  * under the License.
   19  * 
   20  * @APPLE_LICENSE_HEADER_END@
   21  */
   22 /*-
   23  * Copyright (c) 1991, 1993
   24  *      The Regents of the University of California.  All rights reserved.
   25  *
   26  * This code is derived from software contributed to Berkeley by
   27  * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
   28  *
   29  * Redistribution and use in source and binary forms, with or without
   30  * modification, are permitted provided that the following conditions
   31  * are met:
   32  * 1. Redistributions of source code must retain the above copyright
   33  *    notice, this list of conditions and the following disclaimer.
   34  * 2. Redistributions in binary form must reproduce the above copyright
   35  *    notice, this list of conditions and the following disclaimer in the
   36  *    documentation and/or other materials provided with the distribution.
   37  * 3. All advertising materials mentioning features or use of this software
   38  *    must display the following acknowledgement:
   39  *      This product includes software developed by the University of
   40  *      California, Berkeley and its contributors.
   41  * 4. Neither the name of the University nor the names of its contributors
   42  *    may be used to endorse or promote products derived from this software
   43  *    without specific prior written permission.
   44  *
   45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   55  * SUCH DAMAGE.
   56  */
   57 
   58 #if defined(LIBC_SCCS) && !defined(lint)
   59 static char sccsid[] = "@(#)heapsort.c  8.1 (Berkeley) 6/4/93";
   60 #endif /* LIBC_SCCS and not lint */
   61 
   62 
   63 #include <libsa/stdlib.h>
   64 
   65 
   66 /*
   67  * Swap two areas of size number of bytes.  Although qsort(3) permits random
   68  * blocks of memory to be sorted, sorting pointers is almost certainly the
   69  * common case (and, were it not, could easily be made so).  Regardless, it
   70  * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
   71  * arithmetic gets lost in the time required for comparison function calls.
   72  */
   73 #define SWAP(a, b, count, size, tmp) { \
   74         count = size; \
   75         do { \
   76                 tmp = *a; \
   77                 *a++ = *b; \
   78                 *b++ = tmp; \
   79         } while (--count); \
   80 }
   81 
   82 /* Copy one block of size size to another. */
   83 #define COPY(a, b, count, size, tmp1, tmp2) { \
   84         count = size; \
   85         tmp1 = a; \
   86         tmp2 = b; \
   87         do { \
   88                 *tmp1++ = *tmp2++; \
   89         } while (--count); \
   90 }
   91 
   92 /*
   93  * Build the list into a heap, where a heap is defined such that for
   94  * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
   95  *
   96  * There two cases.  If j == nmemb, select largest of Ki and Kj.  If
   97  * j < nmemb, select largest of Ki, Kj and Kj+1.
   98  */
   99 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
  100         for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
  101             par_i = child_i) { \
  102                 child = base + child_i * size; \
  103                 if (child_i < nmemb && compar(child, child + size) < 0) { \
  104                         child += size; \
  105                         ++child_i; \
  106                 } \
  107                 par = base + par_i * size; \
  108                 if (compar(child, par) <= 0) \
  109                         break; \
  110                 SWAP(par, child, count, size, tmp); \
  111         } \
  112 }
  113 
  114 /*
  115  * Select the top of the heap and 'heapify'.  Since by far the most expensive
  116  * action is the call to the compar function, a considerable optimization
  117  * in the average case can be achieved due to the fact that k, the displaced
  118  * elememt, is ususally quite small, so it would be preferable to first
  119  * heapify, always maintaining the invariant that the larger child is copied
  120  * over its parent's record.
  121  *
  122  * Then, starting from the *bottom* of the heap, finding k's correct place,
  123  * again maintianing the invariant.  As a result of the invariant no element
  124  * is 'lost' when k is assigned its correct place in the heap.
  125  *
  126  * The time savings from this optimization are on the order of 15-20% for the
  127  * average case. See Knuth, Vol. 3, page 158, problem 18.
  128  *
  129  * XXX Don't break the #define SELECT line, below.  Reiser cpp gets upset.
  130  */
  131 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
  132         for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
  133                 child = base + child_i * size; \
  134                 if (child_i < nmemb && compar(child, child + size) < 0) { \
  135                         child += size; \
  136                         ++child_i; \
  137                 } \
  138                 par = base + par_i * size; \
  139                 COPY(par, child, count, size, tmp1, tmp2); \
  140         } \
  141         for (;;) { \
  142                 child_i = par_i; \
  143                 par_i = child_i / 2; \
  144                 child = base + child_i * size; \
  145                 par = base + par_i * size; \
  146                 if (child_i == 1 || compar(k, par) < 0) { \
  147                         COPY(child, k, count, size, tmp1, tmp2); \
  148                         break; \
  149                 } \
  150                 COPY(child, par, count, size, tmp1, tmp2); \
  151         } \
  152 }
  153 
  154 /* Pass heapsort off as qsort for krld. -- Nik Gervae
  155  *
  156  * Heapsort -- Knuth, Vol. 3, page 145.  Runs in O (N lg N), both average
  157  * and worst.  While heapsort is faster than the worst case of quicksort,
  158  * the BSD quicksort does median selection so that the chance of finding
  159  * a data set that will trigger the worst case is nonexistent.  Heapsort's
  160  * only advantage over quicksort is that it requires little additional memory.
  161  */
  162 __private_extern__
  163 void qsort(void * vbase, size_t nmemb, size_t size,
  164         int (*compar)(const void *, const void *)) {
  165 
  166         register int cnt, i, j, l;
  167         register char tmp, *tmp1, *tmp2;
  168         char *base, *k, *p, *t;
  169 
  170         if (nmemb <= 1) {
  171             return;
  172         }
  173 
  174         if (!size) {
  175             return;
  176         }
  177 
  178         if ((k = (char *)malloc(size)) == NULL) {
  179 //            panic();
  180             return;
  181         }
  182 
  183         /*
  184          * Items are numbered from 1 to nmemb, so offset from size bytes
  185          * below the starting address.
  186          */
  187         base = (char *)vbase - size;
  188 
  189         for (l = nmemb / 2 + 1; --l;)
  190                 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
  191 
  192         /*
  193          * For each element of the heap, save the largest element into its
  194          * final slot, save the displaced element (k), then recreate the
  195          * heap.
  196          */
  197         while (nmemb > 1) {
  198                 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
  199                 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
  200                 --nmemb;
  201                 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
  202         }
  203         free(k);
  204         return;
  205 }

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