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); 107