/*	$NetBSD: merge.c,v 1.16 2018/05/23 21:21:27 joerg Exp $	*/

/*-
 * 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.
 */

#include <sys/cdefs.h>

/*
 * 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.)
 */

#include <sys/types.h>

#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

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

#define ISIZE sizeof(int)
#define PSIZE sizeof(u_char *)
#define ICOPY_LIST(src, dst, last)                                             \
  do                                                                           \
    *(int *)(void *)dst = *(int *)(void *)src, src += ISIZE, dst += ISIZE;     \
  while (src < last)
#define ICOPY_ELT(src, dst, i)                                                 \
  do                                                                           \
    *(int *)(void *)dst = *(int *)(void *)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)                                                                \
  ((u_char **)(void *)(((uintptr_t)(p) + PSIZE - 1) & ~(PSIZE - 1)))

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

  _DIAGASSERT(base != NULL);
  _DIAGASSERT(cmp != NULL);

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

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

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

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

  list1 = base;
  setup(list1, list2, nmemb, size, cmp);
  last = list2 + nmemb * size;
  i = 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 */
#if 0
LINEAR:
#endif
          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;
#if 0
SLOWCASE:
#endif
          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 = (unsigned int)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;
  }
  free(list2);
  return (0);
}

#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.)
 */

/* XXX: shouldn't this function be static? - lukem 990810 */
void setup(u_char *list1, u_char *list2, size_t n, size_t size,
           int (*cmp)(const void *, const void *)) {
  int length, tmp, sense;
  u_char *f1, *f2, *s, *l2, *last, *p2;
  size_t size2, i;

  _DIAGASSERT(cmp != NULL);
  _DIAGASSERT(list1 != NULL);
  _DIAGASSERT(list2 != NULL);

  size2 = size * 2;
  if (n <= 5) {
    insertionsort(list1, n, size, cmp);
    *EVAL(list2) = 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(u_char *a, size_t n, size_t size,
                          int (*cmp)(const void *, const void *)) {
  u_char *ai, *s, *t, *u, tmp;
  size_t i;

  _DIAGASSERT(a != NULL);
  _DIAGASSERT(cmp != NULL);

  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);
    }
}
