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