/*
* A fast, small, non-recursive O(nlog n) sort for the Linux kernel
*
* Jan 23 2005 Matt Mackall <mpm@selenic.com>
*/
#include <linux/kernel.h>
#include <linux/module.h>
void u32_swap(void *a, void *b, int size)
{
u32 t = *(u32 *)a;
*(u32 *)a = *(u32 *)b;
*(u32 *)b = t;
}
void generic_swap(void *a, void *b, int size)
{
char t;
do {
t = *(char *)a;
*(char *)a++ = *(char *)b;
*(char *)b++ = t;
} while (--size > 0);
}
/*
* sort - sort an array of elements
* @base: pointer to data to sort
* @num: number of elements
* @size: size of each element
* @cmp: pointer to comparison function
* @swap: pointer to swap function or NULL
*
* This function does a heapsort on the given array. You may provide a
* swap function optimized to your element type.
*
* Sorting time is O(n log n) both on average and worst-case. While
* qsort is about 20% faster on average, it suffers from exploitable
* O(n*n) worst-case behavior and extra memory requirements that make
* it less suitable for kernel use.
*/
void sort(void *base, size_t num, size_t size,
int (*cmp)(const void *, const void *),
void (*swap)(void *, void *, int size))
{
/* pre-scale counters for performance */
int i = (num/2) * size, n = num * size, c, r;
if (!swap)
swap = (size == 4 ? u32_swap : generic_swap);
/* heapify */
for ( ; i >= 0; i -= size) {
for (r = i; r * 2 < n; r = c) {
c = r * 2;
if (c < n - size && cmp(base + c, base + c + size) < 0)
c += size;
if (cmp(base + r, base + c) >= 0)
break;
swap(base + r, base + c, size);
}
}
/* sort */
for (i = n - size; i >= 0; i -= size) {
swap(base, base + i, size);
for (r = 0; r * 2 < i; r = c) {
c = r * 2;
if (c < i - size && cmp(base + c, base + c + size) < 0)
c += size;
if (cmp(base + r, base + c) >= 0)
break;
swap(base + r, base + c, size);
}
}
}
EXPORT_SYMBOL(sort);
#if 0
/* a simple boot-time regression test */
int cmpint(const void *a, const void *b)
{
return *(int *)a - *(int *)b;
}
static int sort_test(void)
{
int *a, i, r = 0;
a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
BUG_ON(!a);
printk("testing sort()\n");
for (i = 0; i < 1000; i++) {
r = (r * 725861) % 6599;
a[i] = r;
}
sort(a, 1000, sizeof(int), cmpint, NULL);
for (i = 0; i < 999; i++)
if (a[i] > a[i+1]) {
printk("sort() failed!\n");
break;
}
kfree(a);
return 0;
}
module_init(sort_test);
#endif
