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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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>
Adrian Bunkecec4cb2005-09-10 00:26:59 -07009#include <linux/sort.h>
Tim Schmielau4e57b682005-10-30 15:03:48 -080010#include <linux/slab.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070011
Adrian Bunkecec4cb2005-09-10 00:26:59 -070012static void u32_swap(void *a, void *b, int size)
Linus Torvalds1da177e2005-04-16 15:20:36 -070013{
14 u32 t = *(u32 *)a;
15 *(u32 *)a = *(u32 *)b;
16 *(u32 *)b = t;
17}
18
Adrian Bunkecec4cb2005-09-10 00:26:59 -070019static void generic_swap(void *a, void *b, int size)
Linus Torvalds1da177e2005-04-16 15:20:36 -070020{
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
Robert P. J. Day72fd4a32007-02-10 01:45:59 -080030/**
Linus Torvalds1da177e2005-04-16 15:20:36 -070031 * 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: pointer to comparison function
36 * @swap: pointer to swap function or NULL
37 *
38 * This function does a heapsort on the given array. You may provide a
39 * swap 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
47void sort(void *base, size_t num, size_t size,
48 int (*cmp)(const void *, const void *),
49 void (*swap)(void *, void *, int size))
50{
51 /* pre-scale counters for performance */
keiosd3717bd2006-10-03 01:13:49 -070052 int i = (num/2 - 1) * size, n = num * size, c, r;
Linus Torvalds1da177e2005-04-16 15:20:36 -070053
54 if (!swap)
55 swap = (size == 4 ? u32_swap : generic_swap);
56
57 /* heapify */
58 for ( ; i >= 0; i -= size) {
keiosd3717bd2006-10-03 01:13:49 -070059 for (r = i; r * 2 + size < n; r = c) {
60 c = r * 2 + size;
Linus Torvalds1da177e2005-04-16 15:20:36 -070061 if (c < n - size && cmp(base + c, base + c + size) < 0)
62 c += size;
63 if (cmp(base + r, base + c) >= 0)
64 break;
65 swap(base + r, base + c, size);
66 }
67 }
68
69 /* sort */
Subbaiah Venkata995e4282007-10-16 23:27:06 -070070 for (i = n - size; i > 0; i -= size) {
Linus Torvalds1da177e2005-04-16 15:20:36 -070071 swap(base, base + i, size);
keiosd3717bd2006-10-03 01:13:49 -070072 for (r = 0; r * 2 + size < i; r = c) {
73 c = r * 2 + size;
Linus Torvalds1da177e2005-04-16 15:20:36 -070074 if (c < i - size && cmp(base + c, base + c + size) < 0)
75 c += size;
76 if (cmp(base + r, base + c) >= 0)
77 break;
78 swap(base + r, base + c, size);
79 }
80 }
81}
82
83EXPORT_SYMBOL(sort);
84
85#if 0
86/* a simple boot-time regression test */
87
88int cmpint(const void *a, const void *b)
89{
90 return *(int *)a - *(int *)b;
91}
92
93static int sort_test(void)
94{
Domen Puncerd28c2bc2005-05-05 16:16:19 -070095 int *a, i, r = 1;
Linus Torvalds1da177e2005-04-16 15:20:36 -070096
97 a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
98 BUG_ON(!a);
99
100 printk("testing sort()\n");
101
102 for (i = 0; i < 1000; i++) {
103 r = (r * 725861) % 6599;
104 a[i] = r;
105 }
106
107 sort(a, 1000, sizeof(int), cmpint, NULL);
108
109 for (i = 0; i < 999; i++)
110 if (a[i] > a[i+1]) {
111 printk("sort() failed!\n");
112 break;
113 }
114
115 kfree(a);
116
117 return 0;
118}
119
120module_init(sort_test);
121#endif