Root/lib/sort.c

Source at commit b386be689295730688885552666ea40b2e639b14 created 8 years 11 months ago.
By Maarten ter Huurne, Revert "MIPS: JZ4740: reset: Initialize hibernate wakeup counters."
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
12static 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
19static 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
47void 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
85EXPORT_SYMBOL(sort);
86
87#if 0
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

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