1// SPDX-License-Identifier: GPL-2.0
2/*
3 * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
4 *
5 * Jan 23 2005 Matt Mackall <mpm@selenic.com>
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/types.h>
11#include <linux/export.h>
12#include <linux/sort.h>
13
14static int alignment_ok(const void *base, int align)
15{
16 return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
17 ((unsigned long)base & (align - 1)) == 0;
18}
19
20static void u32_swap(void *a, void *b, int size)
21{
22 u32 t = *(u32 *)a;
23 *(u32 *)a = *(u32 *)b;
24 *(u32 *)b = t;
25}
26
27static void u64_swap(void *a, void *b, int size)
28{
29 u64 t = *(u64 *)a;
30 *(u64 *)a = *(u64 *)b;
31 *(u64 *)b = t;
32}
33
34static void generic_swap(void *a, void *b, int size)
35{
36 char t;
37
38 do {
39 t = *(char *)a;
40 *(char *)a++ = *(char *)b;
41 *(char *)b++ = t;
42 } while (--size > 0);
43}
44
45/**
46 * sort - sort an array of elements
47 * @base: pointer to data to sort
48 * @num: number of elements
49 * @size: size of each element
50 * @cmp_func: pointer to comparison function
51 * @swap_func: pointer to swap function or NULL
52 *
53 * This function does a heapsort on the given array. You may provide a
54 * swap_func function optimized to your element type.
55 *
56 * Sorting time is O(n log n) both on average and worst-case. While
57 * qsort is about 20% faster on average, it suffers from exploitable
58 * O(n*n) worst-case behavior and extra memory requirements that make
59 * it less suitable for kernel use.
60 */
61
62void sort(void *base, size_t num, size_t size,
63 int (*cmp_func)(const void *, const void *),
64 void (*swap_func)(void *, void *, int size))
65{
66 /* pre-scale counters for performance */
67 int i = (num/2 - 1) * size, n = num * size, c, r;
68
69 if (!swap_func) {
70 if (size == 4 && alignment_ok(base, 4))
71 swap_func = u32_swap;
72 else if (size == 8 && alignment_ok(base, 8))
73 swap_func = u64_swap;
74 else
75 swap_func = generic_swap;
76 }
77
78 /* heapify */
79 for ( ; i >= 0; i -= size) {
80 for (r = i; r * 2 + size < n; r = c) {
81 c = r * 2 + size;
82 if (c < n - size &&
83 cmp_func(base + c, base + c + size) < 0)
84 c += size;
85 if (cmp_func(base + r, base + c) >= 0)
86 break;
87 swap_func(base + r, base + c, size);
88 }
89 }
90
91 /* sort */
92 for (i = n - size; i > 0; i -= size) {
93 swap_func(base, base + i, size);
94 for (r = 0; r * 2 + size < i; r = c) {
95 c = r * 2 + size;
96 if (c < i - size &&
97 cmp_func(base + c, base + c + size) < 0)
98 c += size;
99 if (cmp_func(base + r, base + c) >= 0)
100 break;
101 swap_func(base + r, base + c, size);
102 }
103 }
104}
105
106EXPORT_SYMBOL(sort);
107