StdLib/LibC/StdLib/Qsort.c

/** @file
  Quick Sort utility function.

  This utility makes use of a comparison function to search arrays of
  unspecified type. Where an argument declared as size_t nmemb specifies the
  length of the array for a function, nmemb can have the value zero on a call
  to that function; the comparison function is not called, a search finds no
  matching element. Pointer arguments on such a call shall still have valid
  values.

  The implementation shall ensure that both arguments of the comparison
  function are pointers to elements of the array.

  The comparison function shall not alter the contents of the array. The
  implementation may reorder elements of the array between calls to the
  comparison function, but shall not alter the contents of any individual
  element.

  When the same objects (consisting of size bytes, irrespective of their
  current positions in the array) are passed more than once to the comparison
  function, the results shall be consistent with one another. That is, they
  define a total ordering on the array.

  A sequence point occurs immediately before and immediately after each call to
  the comparison function, and also between any call to the comparison function
  and any movement of the objects passed as arguments to that call.

  Copyright (c) 2010, Intel Corporation. All rights reserved.<BR>
 * Copyright (c) 1992, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.

  ("$FreeBSD: src/lib/libc/stdlib/qsort.c,v 1.15.2.1.2.1 2009/10/25 01:10:29 kensmith Exp $");
 */
#include  <LibConfig.h>

#include  <stdlib.h>

typedef int    cmp_t(const void *, const void *);

static __inline char  *med3(char *, char *, char *, cmp_t *);
static __inline void   swapfunc(char *, char *, size_t, int);

/*
 * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
 */
#define swapcode(TYPE, parmi, parmj, n) {     \
  size_t i = (n) / sizeof (TYPE);       \
  TYPE *pi = (TYPE *) (parmi);    \
  TYPE *pj = (TYPE *) (parmj);    \
  do {            \
    TYPE  t = *pi;    \
    *pi++ = *pj;        \
    *pj++ = t;        \
        } while (--i > 0);        \
}

#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
  es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;

static __inline void
swapfunc(char *a, char *b, size_t n, int swaptype)
{
  if(swaptype <= 1)
    swapcode(long, a, b, n)
  else
    swapcode(char, a, b, n)
}

#define swap(a, b)          \
  if (swaptype == 0) {        \
    long t = *(long *)(a);      \
    *(long *)(a) = *(long *)(b);    \
    *(long *)(b) = t;     \
  } else            \
    swapfunc(a, b, es, swaptype)

#define vecswap(a, b, n)  if ((n) > 0) swapfunc(a, b, n, swaptype)

static __inline char *
med3(char *a, char *b, char *c, cmp_t *cmp )
{
  return cmp(a, b) < 0 ?
         (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
              :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
}

/*  The qsort function sorts an array of nmemb objects, the initial element of
    which is pointed to by base.  The size of each object is specified by size.

    The contents of the array are sorted into ascending order according to a
    comparison function pointed to by compar, which is called with two
    arguments that point to the objects being compared. The function shall
    return an integer less than, equal to, or greater than zero if the first
    argument is considered to be respectively less than, equal to, or greater
    than the second.

    If two elements compare as equal, their order in the resulting sorted array
    is unspecified.
*/
void
qsort(void *a, size_t n, size_t es, cmp_t *cmp)
{
  char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
  size_t d, r;
  int cmp_result;
  int swaptype, swap_cnt;

loop: SWAPINIT(a, es);
  swap_cnt = 0;
  if (n < 7) {
    for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
      for (pl = pm;
           pl > (char *)a && cmp(pl - es, pl) > 0;
           pl -= es)
        swap(pl, pl - es);
    return;
  }
  pm = (char *)a + (n / 2) * es;
  if (n > 7) {
    pl = a;
    pn = (char *)a + (n - 1) * es;
    if (n > 40) {
      d = (n / 8) * es;
      pl = med3(pl, pl + d, pl + 2 * d, cmp);
      pm = med3(pm - d, pm, pm + d, cmp);
      pn = med3(pn - 2 * d, pn - d, pn, cmp);
    }
    pm = med3(pl, pm, pn, cmp);
  }
  swap(a, pm);
  pa = pb = (char *)a + es;

  pc = pd = (char *)a + (n - 1) * es;
  for (;;) {
    while (pb <= pc && (cmp_result = cmp(pb, a)) <= 0) {
      if (cmp_result == 0) {
        swap_cnt = 1;
        swap(pa, pb);
        pa += es;
      }
      pb += es;
    }
    while (pb <= pc && (cmp_result = cmp(pc, a)) >= 0) {
      if (cmp_result == 0) {
        swap_cnt = 1;
        swap(pc, pd);
        pd -= es;
      }
      pc -= es;
    }
    if (pb > pc)
      break;
    swap(pb, pc);
    swap_cnt = 1;
    pb += es;
    pc -= es;
  }
  if (swap_cnt == 0) {  /* Switch to insertion sort */
    for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
      for (pl = pm;
           pl > (char *)a && cmp(pl - es, pl) > 0;
           pl -= es)
        swap(pl, pl - es);
    return;
  }

  pn = (char *)a + n * es;
  r = MIN(pa - (char *)a, pb - pa);
  vecswap(a, pb - r, r);
  r = MIN((size_t)(pd - pc), ((size_t)(pn - pd)) - es);
  vecswap(pb, pn - r, r);
  if ((size_t)(r = pb - pa) > es)
    qsort(a, r / es, es, cmp);
  if ((size_t)(r = pd - pc) > es) {
    /* Iterate rather than recurse to save stack space */
    a = pn - r;
    n = r / es;
    goto loop;
  }
/*    qsort(pn - r, r / es, es, cmp);*/
}