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/libkern/qsort.c

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    1 /*-
    2  * Copyright (c) 1992, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 4. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  */
   29 
   30 #include <sys/cdefs.h>
   31 __FBSDID("$FreeBSD: releng/10.4/sys/libkern/qsort.c 319291 2017-05-31 06:26:37Z delphij $");
   32 
   33 #include <sys/param.h>
   34 #include <sys/libkern.h>
   35 
   36 #ifdef I_AM_QSORT_R
   37 typedef int              cmp_t(void *, const void *, const void *);
   38 #else
   39 typedef int              cmp_t(const void *, const void *);
   40 #endif
   41 static inline char      *med3(char *, char *, char *, cmp_t *, void *);
   42 static inline void       swapfunc(char *, char *, size_t, int, int);
   43 
   44 /*
   45  * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
   46  */
   47 #define swapcode(TYPE, parmi, parmj, n) {               \
   48         size_t i = (n) / sizeof (TYPE);                 \
   49         TYPE *pi = (TYPE *) (parmi);            \
   50         TYPE *pj = (TYPE *) (parmj);            \
   51         do {                                            \
   52                 TYPE    t = *pi;                \
   53                 *pi++ = *pj;                            \
   54                 *pj++ = t;                              \
   55         } while (--i > 0);                              \
   56 }
   57 
   58 #define SWAPINIT(TYPE, a, es) swaptype_ ## TYPE =       \
   59         ((char *)a - (char *)0) % sizeof(TYPE) ||       \
   60         es % sizeof(TYPE) ? 2 : es == sizeof(TYPE) ? 0 : 1;
   61 
   62 static inline void
   63 swapfunc(char *a, char *b, size_t n, int swaptype_long, int swaptype_int)
   64 {
   65         if (swaptype_long <= 1)
   66                 swapcode(long, a, b, n)
   67         else if (swaptype_int <= 1)
   68                 swapcode(int, a, b, n)
   69         else
   70                 swapcode(char, a, b, n)
   71 }
   72 
   73 #define swap(a, b)                                      \
   74         if (swaptype_long == 0) {                       \
   75                 long t = *(long *)(a);                  \
   76                 *(long *)(a) = *(long *)(b);            \
   77                 *(long *)(b) = t;                       \
   78         } else if (swaptype_int == 0) {                 \
   79                 int t = *(int *)(a);                    \
   80                 *(int *)(a) = *(int *)(b);              \
   81                 *(int *)(b) = t;                        \
   82         } else                                          \
   83                 swapfunc(a, b, es, swaptype_long, swaptype_int)
   84 
   85 #define vecswap(a, b, n)                                \
   86         if ((n) > 0) swapfunc(a, b, n, swaptype_long, swaptype_int)
   87 
   88 #ifdef I_AM_QSORT_R
   89 #define CMP(t, x, y) (cmp((t), (x), (y)))
   90 #else
   91 #define CMP(t, x, y) (cmp((x), (y)))
   92 #endif
   93 
   94 static inline char *
   95 med3(char *a, char *b, char *c, cmp_t *cmp, void *thunk
   96 #ifndef I_AM_QSORT_R
   97 __unused
   98 #endif
   99 )
  100 {
  101         return CMP(thunk, a, b) < 0 ?
  102                (CMP(thunk, b, c) < 0 ? b : (CMP(thunk, a, c) < 0 ? c : a ))
  103               :(CMP(thunk, b, c) > 0 ? b : (CMP(thunk, a, c) < 0 ? a : c ));
  104 }
  105 
  106 #ifdef I_AM_QSORT_R
  107 void
  108 qsort_r(void *a, size_t n, size_t es, void *thunk, cmp_t *cmp)
  109 #else
  110 #define thunk NULL
  111 void
  112 qsort(void *a, size_t n, size_t es, cmp_t *cmp)
  113 #endif
  114 {
  115         char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
  116         size_t d1, d2;
  117         int cmp_result;
  118         int swaptype_long, swaptype_int, swap_cnt;
  119 
  120 loop:   SWAPINIT(long, a, es);
  121         SWAPINIT(int, a, es);
  122         swap_cnt = 0;
  123         if (n < 7) {
  124                 for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
  125                         for (pl = pm; 
  126                              pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
  127                              pl -= es)
  128                                 swap(pl, pl - es);
  129                 return;
  130         }
  131         pm = (char *)a + (n / 2) * es;
  132         if (n > 7) {
  133                 pl = a;
  134                 pn = (char *)a + (n - 1) * es;
  135                 if (n > 40) {
  136                         size_t d = (n / 8) * es;
  137 
  138                         pl = med3(pl, pl + d, pl + 2 * d, cmp, thunk);
  139                         pm = med3(pm - d, pm, pm + d, cmp, thunk);
  140                         pn = med3(pn - 2 * d, pn - d, pn, cmp, thunk);
  141                 }
  142                 pm = med3(pl, pm, pn, cmp, thunk);
  143         }
  144         swap(a, pm);
  145         pa = pb = (char *)a + es;
  146 
  147         pc = pd = (char *)a + (n - 1) * es;
  148         for (;;) {
  149                 while (pb <= pc && (cmp_result = CMP(thunk, pb, a)) <= 0) {
  150                         if (cmp_result == 0) {
  151                                 swap_cnt = 1;
  152                                 swap(pa, pb);
  153                                 pa += es;
  154                         }
  155                         pb += es;
  156                 }
  157                 while (pb <= pc && (cmp_result = CMP(thunk, pc, a)) >= 0) {
  158                         if (cmp_result == 0) {
  159                                 swap_cnt = 1;
  160                                 swap(pc, pd);
  161                                 pd -= es;
  162                         }
  163                         pc -= es;
  164                 }
  165                 if (pb > pc)
  166                         break;
  167                 swap(pb, pc);
  168                 swap_cnt = 1;
  169                 pb += es;
  170                 pc -= es;
  171         }
  172         if (swap_cnt == 0) {  /* Switch to insertion sort */
  173                 for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
  174                         for (pl = pm; 
  175                              pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
  176                              pl -= es)
  177                                 swap(pl, pl - es);
  178                 return;
  179         }
  180 
  181         pn = (char *)a + n * es;
  182         d1 = MIN(pa - (char *)a, pb - pa);
  183         vecswap(a, pb - d1, d1);
  184         d1 = MIN(pd - pc, pn - pd - es);
  185         vecswap(pb, pn - d1, d1);
  186 
  187         d1 = pb - pa;
  188         d2 = pd - pc;
  189         if (d1 <= d2) {
  190                 /* Recurse on left partition, then iterate on right partition */
  191                 if (d1 > es) {
  192 #ifdef I_AM_QSORT_R
  193                         qsort_r(a, d1 / es, es, thunk, cmp);
  194 #else
  195                         qsort(a, d1 / es, es, cmp);
  196 #endif
  197                 }
  198                 if (d2 > es) {
  199                         /* Iterate rather than recurse to save stack space */
  200                         /* qsort(pn - d2, d2 / es, es, cmp); */
  201                         a = pn - d2;
  202                         n = d2 / es;
  203                         goto loop;
  204                 }
  205         } else {
  206                 /* Recurse on right partition, then iterate on left partition */
  207                 if (d2 > es) {
  208 #ifdef I_AM_QSORT_R
  209                         qsort_r(pn - d2, d2 / es, es, thunk, cmp);
  210 #else
  211                         qsort(pn - d2, d2 / es, es, cmp);
  212 #endif
  213                 }
  214                 if (d1 > es) {
  215                         /* Iterate rather than recurse to save stack space */
  216                         /* qsort(a, d1 / es, es, cmp); */
  217                         n = d1 / es;
  218                         goto loop;
  219                 }
  220         }
  221 }

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