aboutsummaryrefslogtreecommitdiffstats
path: root/lib/sort.c
blob: fc20df42aa6f2945aae8586c3c4d3599ca6d67f0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
/*
 * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
 *
 * Jan 23 2005  Matt Mackall <mpm@selenic.com>
 */

#include <linux/types.h>
#include <linux/export.h>
#include <linux/sort.h>

static int alignment_ok(const void *base, int align)
{
	return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
		((unsigned long)base & (align - 1)) == 0;
}

static void u32_swap(void *a, void *b, int size)
{
	u32 t = *(u32 *)a;
	*(u32 *)a = *(u32 *)b;
	*(u32 *)b = t;
}

static void u64_swap(void *a, void *b, int size)
{
	u64 t = *(u64 *)a;
	*(u64 *)a = *(u64 *)b;
	*(u64 *)b = t;
}

static void generic_swap(void *a, void *b, int size)
{
	char t;

	do {
		t = *(char *)a;
		*(char *)a++ = *(char *)b;
		*(char *)b++ = t;
	} while (--size > 0);
}

/**
 * sort - sort an array of elements
 * @base: pointer to data to sort
 * @num: number of elements
 * @size: size of each element
 * @cmp_func: pointer to comparison function
 * @swap_func: pointer to swap function or NULL
 *
 * This function does a heapsort on the given array. You may provide a
 * swap_func function optimized to your element type.
 *
 * Sorting time is O(n log n) both on average and worst-case. While
 * qsort is about 20% faster on average, it suffers from exploitable
 * O(n*n) worst-case behavior and extra memory requirements that make
 * it less suitable for kernel use.
 */

void sort(void *base, size_t num, size_t size,
	  int (*cmp_func)(const void *, const void *),
	  void (*swap_func)(void *, void *, int size))
{
	/* pre-scale counters for performance */
	int i = (num/2 - 1) * size, n = num * size, c, r;

	if (!swap_func) {
		if (size == 4 && alignment_ok(base, 4))
			swap_func = u32_swap;
		else if (size == 8 && alignment_ok(base, 8))
			swap_func = u64_swap;
		else
			swap_func = generic_swap;
	}

	/* heapify */
	for ( ; i >= 0; i -= size) {
		for (r = i; r * 2 + size < n; r  = c) {
			c = r * 2 + size;
			if (c < n - size &&
					cmp_func(base + c, base + c + size) < 0)
				c += size;
			if (cmp_func(base + r, base + c) >= 0)
				break;
			swap_func(base + r, base + c, size);
		}
	}

	/* sort */
	for (i = n - size; i > 0; i -= size) {
		swap_func(base, base + i, size);
		for (r = 0; r * 2 + size < i; r = c) {
			c = r * 2 + size;
			if (c < i - size &&
					cmp_func(base + c, base + c + size) < 0)
				c += size;
			if (cmp_func(base + r, base + c) >= 0)
				break;
			swap_func(base + r, base + c, size);
		}
	}
}

EXPORT_SYMBOL(sort);

#if 0
#include <linux/slab.h>
/* a simple boot-time regression test */

int cmpint(const void *a, const void *b)
{
	return *(int *)a - *(int *)b;
}

static int sort_test(void)
{
	int *a, i, r = 1;

	a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
	BUG_ON(!a);

	printk("testing sort()\n");

	for (i = 0; i < 1000; i++) {
		r = (r * 725861) % 6599;
		a[i] = r;
	}

	sort(a, 1000, sizeof(int), cmpint, NULL);

	for (i = 0; i < 999; i++)
		if (a[i] > a[i+1]) {
			printk("sort() failed!\n");
			break;
		}

	kfree(a);

	return 0;
}

module_init(sort_test);
#endif

Privacy Policy