1/*
2 * The code of this file was taken from http://jeffreystedfast.blogspot.be,
3 * where it was posted in 2011 by Jeffrey Stedfast under the MIT license.
4 * The MIT license text is as follows:
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to
8 * deal in the Software without restriction, including without limitation the
9 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
10 * sell copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
21 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
22 * IN THE SOFTWARE.
23 */
24
25#include <errno.h>
26#include <string.h>
27#include <stdlib.h>
28#include <isl_sort.h>
29
30#define MID(lo, hi) (lo + ((hi - lo) >> 1))
31
32/* The code here is an optimized merge sort. Starting from a generic merge sort
33 * the following optimizations were applied:
34 *
35 * o Batching of memcpy() calls: Instead of calling memcpy() to copy each and
36 *   every element into a temporary buffer, blocks of elements are copied
37 *   at a time.
38 *
39 * o To reduce the number of memcpy() calls further, copying leading
40 *   and trailing elements into our temporary buffer is avoided, in case it is
41 *   not necessary to merge them.
42 *
43 * A further optimization could be to specialize memcpy calls based on the
44 * size of the types we compare. For now, this code does not include the
45 * relevant optimization, as clang e.g. inlines a very efficient memcpy()
46 * implementation. It is not clear, that the specialized version as provided in
47 * the blog post, is really superior to the one that will be inlined by
48 * default. So we decided to keep the code simple until this optimization was
49 * proven to be beneficial.
50 */
51
52static void
53msort (void *array, void *buf, size_t low, size_t high, size_t size,
54       int (* compare) (const void *, const void *, void *), void *arg)
55{
56    char *a1, *al, *am, *ah, *ls, *hs, *lo, *hi, *b;
57    size_t copied = 0;
58    size_t mid;
59
60    mid = MID (low, high);
61
62    if (mid + 1 < high)
63        msort (array, buf, mid + 1, high, size, compare, arg);
64
65    if (mid > low)
66        msort (array, buf, low, mid, size, compare, arg);
67
68    ah = ((char *) array) + ((high + 1) * size);
69    am = ((char *) array) + ((mid + 1) * size);
70    a1 = al = ((char *) array) + (low * size);
71
72    b = (char *) buf;
73    lo = al;
74    hi = am;
75
76    do {
77        ls = lo;
78        hs = hi;
79
80        if (lo > al || hi > am) {
81            /* our last loop already compared lo & hi and found lo <= hi */
82            lo += size;
83        }
84
85        while (lo < am && compare (lo, hi, arg) <= 0)
86            lo += size;
87
88        if (lo < am) {
89            if (copied == 0) {
90                /* avoid copying the leading items */
91                a1 = lo;
92                ls = lo;
93            }
94
95            /* our last compare tells us hi < lo */
96            hi += size;
97
98            while (hi < ah && compare (hi, lo, arg) < 0)
99                hi += size;
100
101            if (lo > ls) {
102                memcpy (b, ls, lo - ls);
103                copied += (lo - ls);
104                b += (lo - ls);
105            }
106
107            memcpy (b, hs, hi - hs);
108            copied += (hi - hs);
109            b += (hi - hs);
110        } else if (copied) {
111            memcpy (b, ls, lo - ls);
112            copied += (lo - ls);
113            b += (lo - ls);
114
115            /* copy everything we needed to re-order back into array */
116            memcpy (a1, buf, copied);
117            return;
118        } else {
119            /* everything already in order */
120            return;
121        }
122    } while (hi < ah);
123
124    if (lo < am) {
125        memcpy (b, lo, am - lo);
126        copied += (am - lo);
127    }
128
129    memcpy (a1, buf, copied);
130}
131
132static int
133MergeSort (void *base, size_t nmemb, size_t size,
134           int (* compare) (const void *, const void *, void *), void *arg)
135{
136    void *tmp;
137
138    if (nmemb < 2)
139        return 0;
140
141    if (!(tmp = malloc (nmemb * size))) {
142        errno = ENOMEM;
143        return -1;
144    }
145
146    msort (base, tmp, 0, nmemb - 1, size, compare, arg);
147
148    free (tmp);
149
150    return 0;
151}
152
153int isl_sort(void *const pbase, size_t total_elems, size_t size,
154	int (*cmp)(const void *, const void *, void *arg), void *arg)
155{
156    return MergeSort (pbase, total_elems, size, cmp, arg);
157}
158