lib/sort.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
   4  *
   5  * Jan 23 2005  Matt Mackall <mpm@selenic.com>
   6  */
   7
   8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10 #include <linux/types.h>
  11 #include <linux/export.h>
  12 #include <linux/sort.h>
  13
  14 static int alignment_ok(const void *base, int align)
  15 {
  16         return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
  17                 ((unsigned long)base & (align - 1)) == 0;
  18 }
  19
  20 static void u32_swap(void *a, void *b, int size)
  21 {
  22         u32 t = *(u32 *)a;
  23         *(u32 *)a = *(u32 *)b;
  24         *(u32 *)b = t;
  25 }
  26
  27 static void u64_swap(void *a, void *b, int size)
  28 {
  29         u64 t = *(u64 *)a;
  30         *(u64 *)a = *(u64 *)b;
  31         *(u64 *)b = t;
  32 }
  33
  34 static void generic_swap(void *a, void *b, int size)
  35 {
  36         char t;
  37
  38         do {
  39                 t = *(char *)a;
  40                 *(char *)a++ = *(char *)b;
  41                 *(char *)b++ = t;
  42         } while (--size > 0);
  43 }
  44
  45 /**
  46  * sort - sort an array of elements
  47  * @base: pointer to data to sort
  48  * @num: number of elements
  49  * @size: size of each element
  50  * @cmp_func: pointer to comparison function
  51  * @swap_func: pointer to swap function or NULL
  52  *
  53  * This function does a heapsort on the given array. You may provide a
  54  * swap_func function optimized to your element type.
  55  *
  56  * Sorting time is O(n log n) both on average and worst-case. While
  57  * qsort is about 20% faster on average, it suffers from exploitable
  58  * O(n*n) worst-case behavior and extra memory requirements that make
  59  * it less suitable for kernel use.
  60  */
  61
  62 void sort(void *base, size_t num, size_t size,
  63           int (*cmp_func)(const void *, const void *),
  64           void (*swap_func)(void *, void *, int size))
  65 {
  66         /* pre-scale counters for performance */
  67         int i = (num/2 - 1) * size, n = num * size, c, r;
  68
  69         if (!swap_func) {
  70                 if (size == 4 && alignment_ok(base, 4))
  71                         swap_func = u32_swap;
  72                 else if (size == 8 && alignment_ok(base, 8))
  73                         swap_func = u64_swap;
  74                 else
  75                         swap_func = generic_swap;
  76         }
  77
  78         /* heapify */
  79         for ( ; i >= 0; i -= size) {
  80                 for (r = i; r * 2 + size < n; r  = c) {
  81                         c = r * 2 + size;
  82                         if (c < n - size &&
  83                                         cmp_func(base + c, base + c + size) < 0)
  84                                 c += size;
  85                         if (cmp_func(base + r, base + c) >= 0)
  86                                 break;
  87                         swap_func(base + r, base + c, size);
  88                 }
  89         }
  90
  91         /* sort */
  92         for (i = n - size; i > 0; i -= size) {
  93                 swap_func(base, base + i, size);
  94                 for (r = 0; r * 2 + size < i; r = c) {
  95                         c = r * 2 + size;
  96                         if (c < i - size &&
  97                                         cmp_func(base + c, base + c + size) < 0)
  98                                 c += size;
  99                         if (cmp_func(base + r, base + c) >= 0)
 100                                 break;
 101                         swap_func(base + r, base + c, size);
 102                 }
 103         }
 104 }
 105
 106 EXPORT_SYMBOL(sort);