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