LXR linux/lib/sort.c

   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: pointer to comparison function
  36 * @swap: pointer to swap function or NULL
  37 *
  38 * This function does a heapsort on the given array. You may provide a
  39 * swap 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)(const void *, const void *),
  49          void (*swap)(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)
  55                swap = (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 && cmp(base + c, base + c + size) < 0)
  62                                c += size;
  63                        if (cmp(base + r, base + c) >= 0)
  64                                break;
  65                        swap(base + r, base + c, size);
  66                }
  67        }
  68
  69        /* sort */
  70        for (i = n - size; i > 0; i -= size) {
  71                swap(base, base + i, size);
  72                for (r = 0; r * 2 + size < i; r = c) {
  73                        c = r * 2 + size;
  74                        if (c < i - size && cmp(base + c, base + c + size) < 0)
  75                                c += size;
  76                        if (cmp(base + r, base + c) >= 0)
  77                                break;
  78                        swap(base + r, base + c, size);
  79                }
  80        }
  81}
  82
  83EXPORT_SYMBOL(sort);
  84
  85#if 0
  86/* a simple boot-time regression test */
  87
  88int cmpint(const void *a, const void *b)
  89{
  90        return *(int *)a - *(int *)b;
  91}
  92
  93static int sort_test(void)
  94{
  95        int *a, i, r = 1;
  96
  97        a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
  98        BUG_ON(!a);
  99
 100        printk("testing sort()\n");
 101
 102        for (i = 0; i < 1000; i++) {
 103                r = (r * 725861) % 6599;
 104                a[i] = r;
 105        }
 106
 107        sort(a, 1000, sizeof(int), cmpint, NULL);
 108
 109        for (i = 0; i < 999; i++)
 110                if (a[i] > a[i+1]) {
 111                        printk("sort() failed!\n");
 112                        break;
 113                }
 114
 115        kfree(a);
 116
 117        return 0;
 118}
 119
 120module_init(sort_test);
 121#endif
 122