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