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/types.h>
   8 #include <linux/export.h>
   9 #include <linux/sort.h>
  10
  11 static int alignment_ok(const void *base, int align)
  12 {
  13         return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
  14                 ((unsigned long)base & (align - 1)) == 0;
  15 }
  16
  17 static void u32_swap(void *a, void *b, int size)
  18 {
  19         u32 t = *(u32 *)a;
  20         *(u32 *)a = *(u32 *)b;
  21         *(u32 *)b = t;
  22 }
  23
  24 static void u64_swap(void *a, void *b, int size)
  25 {
  26         u64 t = *(u64 *)a;
  27         *(u64 *)a = *(u64 *)b;
  28         *(u64 *)b = t;
  29 }
  30
  31 static void generic_swap(void *a, void *b, int size)
  32 {
  33         char t;
  34
  35         do {
  36                 t = *(char *)a;
  37                 *(char *)a++ = *(char *)b;
  38                 *(char *)b++ = t;
  39         } while (--size > 0);
  40 }
  41
  42 /**
  43  * sort - sort an array of elements
  44  * @base: pointer to data to sort
  45  * @num: number of elements
  46  * @size: size of each element
  47  * @cmp_func: pointer to comparison function
  48  * @swap_func: pointer to swap function or NULL
  49  *
  50  * This function does a heapsort on the given array. You may provide a
  51  * swap_func function optimized to your element type.
  52  *
  53  * Sorting time is O(n log n) both on average and worst-case. While
  54  * qsort is about 20% faster on average, it suffers from exploitable
  55  * O(n*n) worst-case behavior and extra memory requirements that make
  56  * it less suitable for kernel use.
  57  */
  58
  59 void sort(void *base, size_t num, size_t size,
  60           int (*cmp_func)(const void *, const void *),
  61           void (*swap_func)(void *, void *, int size))
  62 {
  63         /* pre-scale counters for performance */
  64         int i = (num/2 - 1) * size, n = num * size, c, r;
  65
  66         if (!swap_func) {
  67                 if (size == 4 && alignment_ok(base, 4))
  68                         swap_func = u32_swap;
  69                 else if (size == 8 && alignment_ok(base, 8))
  70                         swap_func = u64_swap;
  71                 else
  72                         swap_func = generic_swap;
  73         }
  74
  75         /* heapify */
  76         for ( ; i >= 0; i -= size) {
  77                 for (r = i; r * 2 + size < n; r  = c) {
  78                         c = r * 2 + size;
  79                         if (c < n - size &&
  80                                         cmp_func(base + c, base + c + size) < 0)
  81                                 c += size;
  82                         if (cmp_func(base + r, base + c) >= 0)
  83                                 break;
  84                         swap_func(base + r, base + c, size);
  85                 }
  86         }
  87
  88         /* sort */
  89         for (i = n - size; i > 0; i -= size) {
  90                 swap_func(base, base + i, size);
  91                 for (r = 0; r * 2 + size < i; r = c) {
  92                         c = r * 2 + size;
  93                         if (c < i - size &&
  94                                         cmp_func(base + c, base + c + size) < 0)
  95                                 c += size;
  96                         if (cmp_func(base + r, base + c) >= 0)
  97                                 break;
  98                         swap_func(base + r, base + c, size);
  99                 }
 100         }
 101 }
 102
 103 EXPORT_SYMBOL(sort);
 104
 105 #if 0
 106 #include <linux/slab.h>
 107 /* a simple boot-time regression test */
 108
 109 int cmpint(const void *a, const void *b)
 110 {
 111         return *(int *)a - *(int *)b;
 112 }
 113
 114 static int sort_test(void)
 115 {
 116         int *a, i, r = 1;
 117
 118         a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
 119         BUG_ON(!a);
 120
 121         printk("testing sort()\n");
 122
 123         for (i = 0; i < 1000; i++) {
 124                 r = (r * 725861) % 6599;
 125                 a[i] = r;
 126         }
 127
 128         sort(a, 1000, sizeof(int), cmpint, NULL);
 129
 130         for (i = 0; i < 999; i++)
 131                 if (a[i] > a[i+1]) {
 132                         printk("sort() failed!\n");
 133                         break;
 134                 }
 135
 136         kfree(a);
 137
 138         return 0;
 139 }
 140
 141 module_init(sort_test);
 142 #endif