linux/lib/sort.c
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   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_func: pointer to comparison function
  36 * @swap_func: pointer to swap function or NULL
  37 *
  38 * This function does a heapsort on the given array. You may provide a
  39 * swap_func 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_func)(const void *, const void *),
  49          void (*swap_func)(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_func)
  55                swap_func = (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 &&
  62                                        cmp_func(base + c, base + c + size) < 0)
  63                                c += size;
  64                        if (cmp_func(base + r, base + c) >= 0)
  65                                break;
  66                        swap_func(base + r, base + c, size);
  67                }
  68        }
  69
  70        /* sort */
  71        for (i = n - size; i > 0; i -= size) {
  72                swap_func(base, base + i, size);
  73                for (r = 0; r * 2 + size < i; r = c) {
  74                        c = r * 2 + size;
  75                        if (c < i - size &&
  76                                        cmp_func(base + c, base + c + size) < 0)
  77                                c += size;
  78                        if (cmp_func(base + r, base + c) >= 0)
  79                                break;
  80                        swap_func(base + r, base + c, size);
  81                }
  82        }
  83}
  84
  85EXPORT_SYMBOL(sort);
  86
  87#if 0
  88/* a simple boot-time regression test */
  89
  90int cmpint(const void *a, const void *b)
  91{
  92        return *(int *)a - *(int *)b;
  93}
  94
  95static int sort_test(void)
  96{
  97        int *a, i, r = 1;
  98
  99        a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
 100        BUG_ON(!a);
 101
 102        printk("testing sort()\n");
 103
 104        for (i = 0; i < 1000; i++) {
 105                r = (r * 725861) % 6599;
 106                a[i] = r;
 107        }
 108
 109        sort(a, 1000, sizeof(int), cmpint, NULL);
 110
 111        for (i = 0; i < 999; i++)
 112                if (a[i] > a[i+1]) {
 113                        printk("sort() failed!\n");
 114                        break;
 115                }
 116
 117        kfree(a);
 118
 119        return 0;
 120}
 121
 122module_init(sort_test);
 123#endif
 124
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