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+/* $OpenBSD: merge.c,v 1.10 2015/06/21 03:20:56 millert 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.
+ */
+
+/*
+ * 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 <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+static void setup(u_char *list1, u_char *list2, size_t n, size_t size,
+ int (*cmp)(const void *, const void *));
+static void insertionsort(u_char *a, size_t n, size_t size,
+ int (*cmp)(const void *, const void *));
+
+#define ISIZE sizeof(int)
+#define PSIZE sizeof(u_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) (u_char **) \
+ ((u_char *)0 + \
+ (((u_char *)p + PSIZE - 1 - (u_char *) 0) & ~(PSIZE - 1)))
+
+/*
+ * Arguments are as for qsort.
+ */
+int
+mergesort(void *base, size_t nmemb, size_t size,
+ int (*cmp)(const void *, const void *))
+{
+ int i, sense;
+ int big, iflag;
+ u_char *f1, *f2, *t, *b, *tp2, *q, *l1, *l2;
+ u_char *list2, *list1, *p2, *p, *last, **p1;
+
+ 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) && !(((char *)base - (char *)0) % 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 */
+ 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;
+ }
+ 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.)
+ */
+void
+setup(u_char *list1, u_char *list2, size_t n, size_t size,
+ int (*cmp)(const void *, const void *))
+{
+ int i, length, size2, sense;
+ u_char tmp, *f1, *f2, *s, *l2, *last, *p2;
+
+ size2 = size*2;
+ if (n <= 5) {
+ insertionsort(list1, n, size, cmp);
+ *EVAL(list2) = (u_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(u_char *a, size_t n, size_t size,
+ int (*cmp)(const void *, const void *))
+{
+ u_char *ai, *s, *t, *u, tmp;
+ int 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);
+ }
+}
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