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 121