root/lib/sort.c

DEFINITIONS

1. u32_swap
2. generic_swap
3. sort
4. cmpint
5. sort_test

/*
 * 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