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mergesort.c

/*
 * mergesort() implementation for systems that don't have it.
 *
 * Copyright (c) 1992, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Peter McIlroy.
 *
 * 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.
 * 3. 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.
 */
#define YASM_LIB_INTERNAL
#include "util.h"
/*@unused@*/ RCSID("$Id: mergesort.c 1137 2004-09-04 01:24:57Z peter $");

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)merge.c 8.2 (Berkeley) 2/14/94";
#endif /* LIBC_SCCS and not lint */

#ifdef HAVE_MERGESORT
#undef yasm__mergesort
#endif

#ifndef HAVE_MERGESORT
/*
 * Hybrid exponential search/linear search merge sort with hybrid
 * natural/pairwise first pass.  Requires about .3% more comparisons
 * for random data than LSMS with pairwise first pass alone.
 * It works for objects as small as two bytes.
 */

#define NATURAL
#define THRESHOLD 16    /* Best choice for natural merge cut-off. */

/* #define NATURAL to get hybrid natural merge.
 * (The default is pairwise merging.)
 */

#ifdef STDC_HEADERS
# include <errno.h>
# include <string.h>
#endif

static void setup(unsigned char *, unsigned char *, size_t, size_t,
              int (*)(const void *, const void *));
static void insertionsort(unsigned char *, size_t, size_t,
                    int (*)(const void *, const void *));

#define ISIZE sizeof(int)
#define PSIZE sizeof(unsigned char *)
#define ICOPY_LIST(src, dst, last)                    \
      do                                        \
      *(int*)dst = *(int*)src, src += ISIZE, dst += ISIZE;  \
      while(src < last)
#define ICOPY_ELT(src, dst, i)                              \
      do                                        \
      *(int*) dst = *(int*) src, src += ISIZE, dst += ISIZE;      \
      while (i -= ISIZE)

#define CCOPY_LIST(src, dst, last)        \
      do                            \
            *dst++ = *src++;        \
      while (src < last)
#define CCOPY_ELT(src, dst, i)                  \
      do                            \
            *dst++ = *src++;        \
      while (i -= 1)

/*
 * Find the next possible pointer head.  (Trickery for forcing an array
 * to do double duty as a linked list when objects do not align with word
 * boundaries.
 */
/* Assumption: PSIZE is a power of 2. */
#define EVAL(p) (unsigned char **)                                \
      ((unsigned char *)0 +                                       \
          (((unsigned char *)p + PSIZE - 1 - (unsigned char *) 0) & ~(PSIZE - 1)))
#endif      /*HAVE_MERGESORT*/

/*
 * Arguments are as for qsort.
 */
int
00106 yasm__mergesort(void *base, size_t nmemb, size_t size,
            int (*cmp)(const void *, const void *))
{
#ifdef HAVE_MERGESORT
    return mergesort(base, nmemb, size, cmp);
#else
      size_t i;
      int sense;
      int big, iflag;
      unsigned char *f1, *f2, *t, *b, *tp2, *q, *l1, *l2;
      unsigned char *list2, *list1, *p2, *p, *last, **p1;

      if (size < PSIZE / 2) {       /* Pointers must fit into 2 * size. */
#ifdef EINVAL
            errno = EINVAL;
#endif
            return (-1);
      }

      if (nmemb == 0)
            return (0);

      /*
       * XXX
       * Stupid subtraction for the Cray.
       */
      iflag = 0;
      if (!(size % ISIZE) && !(((char *)base - (char *)0) % ISIZE))
            iflag = 1;

      if ((list2 = yasm_xmalloc(nmemb * size + PSIZE)) == NULL)
            return (-1);

      list1 = base;
      setup(list1, list2, nmemb, size, cmp);
      last = list2 + nmemb * size;
      i = 0;
      big = 0;
      while (*EVAL(list2) != last) {
          l2 = list1;
          p1 = EVAL(list1);
          for (tp2 = p2 = list2; p2 != last; p1 = EVAL(l2)) {
            p2 = *EVAL(p2);
            f1 = l2;
            f2 = l1 = list1 + (p2 - list2);
            if (p2 != last)
                  p2 = *EVAL(p2);
            l2 = list1 + (p2 - list2);
            while (f1 < l1 && f2 < l2) {
                  if ((*cmp)(f1, f2) <= 0) {
                        q = f2;
                        b = f1, t = l1;
                        sense = -1;
                  } else {
                        q = f1;
                        b = f2, t = l2;
                        sense = 0;
                  }
                  if (!big) { /* here i = 0 */
                        while ((b += size) < t && cmp(q, b) >sense)
                              if (++i == 6) {
                                    big = 1;
                                    goto EXPONENTIAL;
                              }
                  } else {
EXPONENTIAL:                  for (i = size; ; i <<= 1)
                              if ((p = (b + i)) >= t) {
                                    if ((p = t - size) > b &&
                                        (*cmp)(q, p) <= sense)
                                          t = p;
                                    else
                                          b = p;
                                    break;
                              } else if ((*cmp)(q, p) <= sense) {
                                    t = p;
                                    if (i == size)
                                          big = 0;
                                    goto FASTCASE;
                              } else
                                    b = p;
                        while (t > b+size) {
                              i = (((t - b) / size) >> 1) * size;
                              if ((*cmp)(q, p = b + i) <= sense)
                                    t = p;
                              else
                                    b = p;
                        }
                        goto COPY;
FASTCASE:               while (i > size)
                              if ((*cmp)(q,
                                    p = b + (i >>= 1)) <= sense)
                                    t = p;
                              else
                                    b = p;
COPY:                   b = t;
                  }
                  i = size;
                  if (q == f1) {
                        if (iflag) {
                              ICOPY_LIST(f2, tp2, b);
                              ICOPY_ELT(f1, tp2, i);
                        } else {
                              CCOPY_LIST(f2, tp2, b);
                              CCOPY_ELT(f1, tp2, i);
                        }
                  } else {
                        if (iflag) {
                              ICOPY_LIST(f1, tp2, b);
                              ICOPY_ELT(f2, tp2, i);
                        } else {
                              CCOPY_LIST(f1, tp2, b);
                              CCOPY_ELT(f2, tp2, i);
                        }
                  }
            }
            if (f2 < l2) {
                  if (iflag)
                        ICOPY_LIST(f2, tp2, l2);
                  else
                        CCOPY_LIST(f2, tp2, l2);
            } else if (f1 < l1) {
                  if (iflag)
                        ICOPY_LIST(f1, tp2, l1);
                  else
                        CCOPY_LIST(f1, tp2, l1);
            }
            *p1 = l2;
          }
          tp2 = list1;  /* swap list1, list2 */
          list1 = list2;
          list2 = tp2;
          last = list2 + nmemb*size;
      }
      if (base == list2) {
            memmove(list2, list1, nmemb*size);
            list2 = list1;
      }
      yasm_xfree(list2);
      return (0);
#endif      /*HAVE_MERGESORT*/
}

#ifndef HAVE_MERGESORT

#define     swap(a, b) {                              \
            s = b;                              \
            i = size;                     \
            do {                          \
                  tmp = *a; *a++ = *s; *s++ = tmp; \
            } while (--i);                      \
            a -= size;                    \
      }
#define reverse(bot, top) {                     \
      s = top;                            \
      do {                                \
            i = size;                     \
            do {                          \
                  tmp = *bot; *bot++ = *s; *s++ = tmp; \
            } while (--i);                      \
            s -= size2;                   \
      } while(bot < s);                   \
}

/*
 * Optional hybrid natural/pairwise first pass.  Eats up list1 in runs of
 * increasing order, list2 in a corresponding linked list.  Checks for runs
 * when THRESHOLD/2 pairs compare with same sense.  (Only used when NATURAL
 * is defined.  Otherwise simple pairwise merging is used.)
 */
void
setup(unsigned char *list1, unsigned char *list2, size_t n, size_t size,
      int (*cmp)(const void *, const void *))
{
      size_t i;
      unsigned int tmp;
      int length, size2, sense;
      unsigned char *f1, *f2, *s, *l2, *last, *p2;

      size2 = size*2;
      if (n <= 5) {
            insertionsort(list1, n, size, cmp);
            *EVAL(list2) = (unsigned char*) list2 + n*size;
            return;
      }
      /*
       * Avoid running pointers out of bounds; limit n to evens
       * for simplicity.
       */
      i = 4 + (n & 1);
      insertionsort(list1 + (n - i) * size, i, size, cmp);
      last = list1 + size * (n - i);
      *EVAL(list2 + (last - list1)) = list2 + n * size;

#ifdef NATURAL
      p2 = list2;
      f1 = list1;
      sense = (cmp(f1, f1 + size) > 0);
      for (; f1 < last; sense = !sense) {
            length = 2;
                              /* Find pairs with same sense. */
            for (f2 = f1 + size2; f2 < last; f2 += size2) {
                  if ((cmp(f2, f2+ size) > 0) != sense)
                        break;
                  length += 2;
            }
            if (length < THRESHOLD) {           /* Pairwise merge */
                  do {
                        p2 = *EVAL(p2) = f1 + size2 - list1 + list2;
                        if (sense > 0)
                              swap (f1, f1 + size);
                  } while ((f1 += size2) < f2);
            } else {                      /* Natural merge */
                  l2 = f2;
                  for (f2 = f1 + size2; f2 < l2; f2 += size2) {
                        if ((cmp(f2-size, f2) > 0) != sense) {
                              p2 = *EVAL(p2) = f2 - list1 + list2;
                              if (sense > 0)
                                    reverse(f1, f2-size);
                              f1 = f2;
                        }
                  }
                  if (sense > 0)
                        reverse (f1, f2-size);
                  f1 = f2;
                  if (f2 < last || cmp(f2 - size, f2) > 0)
                        p2 = *EVAL(p2) = f2 - list1 + list2;
                  else
                        p2 = *EVAL(p2) = list2 + n*size;
            }
      }
#else       /* pairwise merge only. */
      for (f1 = list1, p2 = list2; f1 < last; f1 += size2) {
            p2 = *EVAL(p2) = p2 + size2;
            if (cmp (f1, f1 + size) > 0)
                  swap(f1, f1 + size);
      }
#endif /* NATURAL */
}

/*
 * This is to avoid out-of-bounds addresses in sorting the
 * last 4 elements.
 */
static void
insertionsort(unsigned char *a, size_t n, size_t size,
            int (*cmp)(const void *, const void *))
{
      unsigned char *ai, *s, *t, *u, tmp;
      size_t i;

      for (ai = a+size; --n >= 1; ai += size)
            for (t = ai; t > a; t -= size) {
                  u = t - size;
                  if (cmp(u, t) <= 0)
                        break;
                  swap(u, t);
            }
}
#endif      /*HAVE_MERGESORT*/

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