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/*

 * 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>

#include <linux/sort.h>

#include <linux/slab.h>

static void u32_swap(void *a, void *b, int size)

{

        u32 t = *(u32 *)a;

        *(u32 *)a = *(u32 *)b;

        *(u32 *)b = t;

}

static 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 - 1) * 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 + size < n; r  = c) {

                        c = r * 2 + size;

                        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 + size < i; r = c) {

                        c = r * 2 + size;

                        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 = 1;

        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