sort.c

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/*
 * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
 *
 * Jan 23 2005  Matt Mackall <[email protected]>
 */

#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);
}

void sort(void *base, size_t num, size_t size,
      int (*cmp_func)(const void *, const void *),
      void (*swap_func)(void *, void *, int size))
{
    /* pre-scale counters for performance */
    int i = (num/2 - 1) * size, n = num * size, c, r;

    if (!swap_func)
        swap_func = (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_func(base + c, base + c + size) < 0)
                c += size;
            if (cmp_func(base + r, base + c) >= 0)
                break;
            swap_func(base + r, base + c, size);
        }
    }

    /* sort */
    for (i = n - size; i > 0; i -= size) {
        swap_func(base, base + i, size);
        for (r = 0; r * 2 + size < i; r = c) {
            c = r * 2 + size;
            if (c < i - size &&
                    cmp_func(base + c, base + c + size) < 0)
                c += size;
            if (cmp_func(base + r, base + c) >= 0)
                break;
            swap_func(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