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
  10 void u32_swap(void *a, void *b, int size)
  11 {
  12         u32 t = *(u32 *)a;
  13         *(u32 *)a = *(u32 *)b;
  14         *(u32 *)b = t;
  15 }
  16
  17 void generic_swap(void *a, void *b, int size)
  18 {
  19         char t;
  20
  21         do {
  22                 t = *(char *)a;
  23                 *(char *)a++ = *(char *)b;
  24                 *(char *)b++ = t;
  25         } while (--size > 0);
  26 }
  27
  28 /*
  29  * sort - sort an array of elements
  30  * @base: pointer to data to sort
  31  * @num: number of elements
  32  * @size: size of each element
  33  * @cmp: pointer to comparison function
  34  * @swap: pointer to swap function or NULL
  35  *
  36  * This function does a heapsort on the given array. You may provide a
  37  * swap function optimized to your element type.
  38  *
  39  * Sorting time is O(n log n) both on average and worst-case. While
  40  * qsort is about 20% faster on average, it suffers from exploitable
  41  * O(n*n) worst-case behavior and extra memory requirements that make
  42  * it less suitable for kernel use.
  43  */
  44
  45 void sort(void *base, size_t num, size_t size,
  46           int (*cmp)(const void *, const void *),
  47           void (*swap)(void *, void *, int size))
  48 {
  49         /* pre-scale counters for performance */
  50         int i = (num/2) * size, n = num * size, c, r;
  51
  52         if (!swap)
  53                 swap = (size == 4 ? u32_swap : generic_swap);
  54
  55         /* heapify */
  56         for ( ; i >= 0; i -= size) {
  57                 for (r = i; r * 2 < n; r  = c) {
  58                         c = r * 2;
  59                         if (c < n - size && cmp(base + c, base + c + size) < 0)
  60                                 c += size;
  61                         if (cmp(base + r, base + c) >= 0)
  62                                 break;
  63                         swap(base + r, base + c, size);
  64                 }
  65         }
  66
  67         /* sort */
  68         for (i = n - size; i >= 0; i -= size) {
  69                 swap(base, base + i, size);
  70                 for (r = 0; r * 2 < i; r = c) {
  71                         c = r * 2;
  72                         if (c < i - size && cmp(base + c, base + c + size) < 0)
  73                                 c += size;
  74                         if (cmp(base + r, base + c) >= 0)
  75                                 break;
  76                         swap(base + r, base + c, size);
  77                 }
  78         }
  79 }
  80
  81 EXPORT_SYMBOL(sort);
  82
  83 #if 0
  84 /* a simple boot-time regression test */
  85
  86 int cmpint(const void *a, const void *b)
  87 {
  88         return *(int *)a - *(int *)b;
  89 }
  90
  91 static int sort_test(void)
  92 {
  93         int *a, i, r = 1;
  94
  95         a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
  96         BUG_ON(!a);
  97
  98         printk("testing sort()\n");
  99
 100         for (i = 0; i < 1000; i++) {
 101                 r = (r * 725861) % 6599;
 102                 a[i] = r;
 103         }
 104
 105         sort(a, 1000, sizeof(int), cmpint, NULL);
 106
 107         for (i = 0; i < 999; i++)
 108                 if (a[i] > a[i+1]) {
 109                         printk("sort() failed!\n");
 110                         break;
 111                 }
 112
 113         kfree(a);
 114
 115         return 0;
 116 }
 117
 118 module_init(sort_test);
 119 #endif