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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   8
   9 #include <linux/types.h>
  10 #include <linux/export.h>
  11 #include <linux/sort.h>
  12
  13 static int alignment_ok(const void *base, int align)
  14 {
  15         return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
  16                 ((unsigned long)base & (align - 1)) == 0;
  17 }
  18
  19 static void u32_swap(void *a, void *b, int size)
  20 {
  21         u32 t = *(u32 *)a;
  22         *(u32 *)a = *(u32 *)b;
  23         *(u32 *)b = t;
  24 }
  25
  26 static void u64_swap(void *a, void *b, int size)
  27 {
  28         u64 t = *(u64 *)a;
  29         *(u64 *)a = *(u64 *)b;
  30         *(u64 *)b = t;
  31 }
  32
  33 static void generic_swap(void *a, void *b, int size)
  34 {
  35         char t;
  36
  37         do {
  38                 t = *(char *)a;
  39                 *(char *)a++ = *(char *)b;
  40                 *(char *)b++ = t;
  41         } while (--size > 0);
  42 }
  43
  44 /**
  45  * sort - sort an array of elements
  46  * @base: pointer to data to sort
  47  * @num: number of elements
  48  * @size: size of each element
  49  * @cmp_func: pointer to comparison function
  50  * @swap_func: pointer to swap function or NULL
  51  *
  52  * This function does a heapsort on the given array. You may provide a
  53  * swap_func function optimized to your element type.
  54  *
  55  * Sorting time is O(n log n) both on average and worst-case. While
  56  * qsort is about 20% faster on average, it suffers from exploitable
  57  * O(n*n) worst-case behavior and extra memory requirements that make
  58  * it less suitable for kernel use.
  59  */
  60
  61 void sort(void *base, size_t num, size_t size,
  62           int (*cmp_func)(const void *, const void *),
  63           void (*swap_func)(void *, void *, int size))
  64 {
  65         /* pre-scale counters for performance */
  66         int i = (num/2 - 1) * size, n = num * size, c, r;
  67
  68         if (!swap_func) {
  69                 if (size == 4 && alignment_ok(base, 4))
  70                         swap_func = u32_swap;
  71                 else if (size == 8 && alignment_ok(base, 8))
  72                         swap_func = u64_swap;
  73                 else
  74                         swap_func = generic_swap;
  75         }
  76
  77         /* heapify */
  78         for ( ; i >= 0; i -= size) {
  79                 for (r = i; r * 2 + size < n; r  = c) {
  80                         c = r * 2 + size;
  81                         if (c < n - size &&
  82                                         cmp_func(base + c, base + c + size) < 0)
  83                                 c += size;
  84                         if (cmp_func(base + r, base + c) >= 0)
  85                                 break;
  86                         swap_func(base + r, base + c, size);
  87                 }
  88         }
  89
  90         /* sort */
  91         for (i = n - size; i > 0; i -= size) {
  92                 swap_func(base, base + i, size);
  93                 for (r = 0; r * 2 + size < i; r = c) {
  94                         c = r * 2 + size;
  95                         if (c < i - size &&
  96                                         cmp_func(base + c, base + c + size) < 0)
  97                                 c += size;
  98                         if (cmp_func(base + r, base + c) >= 0)
  99                                 break;
 100                         swap_func(base + r, base + c, size);
 101                 }
 102         }
 103 }
 104
 105 EXPORT_SYMBOL(sort);