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