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
  12 static 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
  19 static 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
  47 void 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
  83 EXPORT_SYMBOL(sort);
  84
  85 #if 0
  86 /* a simple boot-time regression test */
  87
  88 int cmpint(const void *a, const void *b)
  89 {
  90         return *(int *)a - *(int *)b;
  91 }
  92
  93 static 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
 120 module_init(sort_test);
 121 #endif