1/*
2 * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
3 *
4 * Jan 23 2005  Matt Mackall <mpm@selenic.com>
5 */
6
7#include <linux/types.h>
8#include <linux/export.h>
9#include <linux/sort.h>
10
11static int alignment_ok(const void *base, int align)
12{
13	return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
14		((unsigned long)base & (align - 1)) == 0;
15}
16
17static void u32_swap(void *a, void *b, int size)
18{
19	u32 t = *(u32 *)a;
20	*(u32 *)a = *(u32 *)b;
21	*(u32 *)b = t;
22}
23
24static void u64_swap(void *a, void *b, int size)
25{
26	u64 t = *(u64 *)a;
27	*(u64 *)a = *(u64 *)b;
28	*(u64 *)b = t;
29}
30
31static void generic_swap(void *a, void *b, int size)
32{
33	char t;
34
35	do {
36		t = *(char *)a;
37		*(char *)a++ = *(char *)b;
38		*(char *)b++ = t;
39	} while (--size > 0);
40}
41
42/**
43 * sort - sort an array of elements
44 * @base: pointer to data to sort
45 * @num: number of elements
46 * @size: size of each element
47 * @cmp_func: pointer to comparison function
48 * @swap_func: pointer to swap function or NULL
49 *
50 * This function does a heapsort on the given array. You may provide a
51 * swap_func function optimized to your element type.
52 *
53 * Sorting time is O(n log n) both on average and worst-case. While
54 * qsort is about 20% faster on average, it suffers from exploitable
55 * O(n*n) worst-case behavior and extra memory requirements that make
56 * it less suitable for kernel use.
57 */
58
59void sort(void *base, size_t num, size_t size,
60	  int (*cmp_func)(const void *, const void *),
61	  void (*swap_func)(void *, void *, int size))
62{
63	/* pre-scale counters for performance */
64	int i = (num/2 - 1) * size, n = num * size, c, r;
65
66	if (!swap_func) {
67		if (size == 4 && alignment_ok(base, 4))
68			swap_func = u32_swap;
69		else if (size == 8 && alignment_ok(base, 8))
70			swap_func = u64_swap;
71		else
72			swap_func = generic_swap;
73	}
74
75	/* heapify */
76	for ( ; i >= 0; i -= size) {
77		for (r = i; r * 2 + size < n; r  = c) {
78			c = r * 2 + size;
79			if (c < n - size &&
80					cmp_func(base + c, base + c + size) < 0)
81				c += size;
82			if (cmp_func(base + r, base + c) >= 0)
83				break;
84			swap_func(base + r, base + c, size);
85		}
86	}
87
88	/* sort */
89	for (i = n - size; i > 0; i -= size) {
90		swap_func(base, base + i, size);
91		for (r = 0; r * 2 + size < i; r = c) {
92			c = r * 2 + size;
93			if (c < i - size &&
94					cmp_func(base + c, base + c + size) < 0)
95				c += size;
96			if (cmp_func(base + r, base + c) >= 0)
97				break;
98			swap_func(base + r, base + c, size);
99		}
100	}
101}
102
103EXPORT_SYMBOL(sort);
104
105#if 0
106#include <linux/slab.h>
107/* a simple boot-time regression test */
108
109int cmpint(const void *a, const void *b)
110{
111	return *(int *)a - *(int *)b;
112}
113
114static int sort_test(void)
115{
116	int *a, i, r = 1;
117
118	a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
119	BUG_ON(!a);
120
121	printk("testing sort()\n");
122
123	for (i = 0; i < 1000; i++) {
124		r = (r * 725861) % 6599;
125		a[i] = r;
126	}
127
128	sort(a, 1000, sizeof(int), cmpint, NULL);
129
130	for (i = 0; i < 999; i++)
131		if (a[i] > a[i+1]) {
132			printk("sort() failed!\n");
133			break;
134		}
135
136	kfree(a);
137
138	return 0;
139}
140
141module_init(sort_test);
142#endif
143