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); 106