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Linux/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
143 

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