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