1/* sort.c -- Sort without allocating memory
2 Copyright (C) 2012-2025 Free Software Foundation, Inc.
3 Written by Ian Lance Taylor, Google.
4
5Redistribution and use in source and binary forms, with or without
6modification, are permitted provided that the following conditions are
7met:
8
9 (1) Redistributions of source code must retain the above copyright
10 notice, this list of conditions and the following disclaimer.
11
12 (2) Redistributions in binary form must reproduce the above copyright
13 notice, this list of conditions and the following disclaimer in
14 the documentation and/or other materials provided with the
15 distribution.
16
17 (3) The name of the author may not be used to
18 endorse or promote products derived from this software without
19 specific prior written permission.
20
21THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
22IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
23WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
24DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
25INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
26(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
27SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
29STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
30IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
31POSSIBILITY OF SUCH DAMAGE. */
32
33#include "config.h"
34
35#include <stddef.h>
36#include <sys/types.h>
37
38#include "backtrace.h"
39#include "internal.h"
40
41/* The GNU glibc version of qsort allocates memory, which we must not
42 do if we are invoked by a signal handler. So provide our own
43 sort. */
44
45static void
46swap (char *a, char *b, size_t size)
47{
48 size_t i;
49
50 for (i = 0; i < size; i++, a++, b++)
51 {
52 char t;
53
54 t = *a;
55 *a = *b;
56 *b = t;
57 }
58}
59
60void
61backtrace_qsort (void *basearg, size_t count, size_t size,
62 int (*compar) (const void *, const void *))
63{
64 char *base = (char *) basearg;
65 size_t i;
66 size_t mid;
67
68 tail_recurse:
69 if (count < 2)
70 return;
71
72 /* The symbol table and DWARF tables, which is all we use this
73 routine for, tend to be roughly sorted. Pick the middle element
74 in the array as our pivot point, so that we are more likely to
75 cut the array in half for each recursion step. */
76 swap (a: base, b: base + (count / 2) * size, size);
77
78 mid = 0;
79 for (i = 1; i < count; i++)
80 {
81 if ((*compar) (base, base + i * size) > 0)
82 {
83 ++mid;
84 if (i != mid)
85 swap (a: base + mid * size, b: base + i * size, size);
86 }
87 }
88
89 if (mid > 0)
90 swap (a: base, b: base + mid * size, size);
91
92 /* Recurse with the smaller array, loop with the larger one. That
93 ensures that our maximum stack depth is log count. */
94 if (2 * mid < count)
95 {
96 backtrace_qsort (basearg: base, count: mid, size, compar);
97 base += (mid + 1) * size;
98 count -= mid + 1;
99 goto tail_recurse;
100 }
101 else
102 {
103 backtrace_qsort (basearg: base + (mid + 1) * size, count: count - (mid + 1),
104 size, compar);
105 count = mid;
106 goto tail_recurse;
107 }
108}
109

source code of libbacktrace/sort.c