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
alignment_ok(const void * base,int align)11 static 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
u32_swap(void * a,void * b,int size)17 static 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
u64_swap(void * a,void * b,int size)24 static 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
generic_swap(void * a,void * b,int size)31 static 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
sort(void * base,size_t num,size_t size,int (* cmp_func)(const void *,const void *),void (* swap_func)(void *,void *,int size))59 void 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
103 EXPORT_SYMBOL(sort);
104
105 #if 0
106 #include <linux/slab.h>
107 /* a simple boot-time regression test */
108
109 int cmpint(const void *a, const void *b)
110 {
111 return *(int *)a - *(int *)b;
112 }
113
114 static 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
141 module_init(sort_test);
142 #endif
143