107 lines
2.5 KiB
C
107 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* A fast, small, non-recursive O(nlog n) sort for the Linux kernel
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*
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* Jan 23 2005 Matt Mackall <mpm@selenic.com>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/types.h>
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#include <linux/export.h>
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#include <linux/sort.h>
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static int alignment_ok(const void *base, int align)
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{
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return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
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((unsigned long)base & (align - 1)) == 0;
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}
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static void u32_swap(void *a, void *b, int size)
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{
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u32 t = *(u32 *)a;
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*(u32 *)a = *(u32 *)b;
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*(u32 *)b = t;
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}
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static void u64_swap(void *a, void *b, int size)
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{
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u64 t = *(u64 *)a;
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*(u64 *)a = *(u64 *)b;
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*(u64 *)b = t;
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}
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static void generic_swap(void *a, void *b, int size)
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{
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char t;
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do {
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t = *(char *)a;
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*(char *)a++ = *(char *)b;
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*(char *)b++ = t;
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} while (--size > 0);
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}
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/**
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* sort - sort an array of elements
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* @base: pointer to data to sort
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* @num: number of elements
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* @size: size of each element
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* @cmp_func: pointer to comparison function
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* @swap_func: pointer to swap function or NULL
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*
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* This function does a heapsort on the given array. You may provide a
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* swap_func function optimized to your element type.
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*
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* Sorting time is O(n log n) both on average and worst-case. While
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* qsort is about 20% faster on average, it suffers from exploitable
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* O(n*n) worst-case behavior and extra memory requirements that make
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* it less suitable for kernel use.
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*/
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void sort(void *base, size_t num, size_t size,
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int (*cmp_func)(const void *, const void *),
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void (*swap_func)(void *, void *, int size))
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{
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/* pre-scale counters for performance */
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int i = (num/2 - 1) * size, n = num * size, c, r;
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if (!swap_func) {
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if (size == 4 && alignment_ok(base, 4))
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swap_func = u32_swap;
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else if (size == 8 && alignment_ok(base, 8))
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swap_func = u64_swap;
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else
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swap_func = generic_swap;
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}
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/* heapify */
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for ( ; i >= 0; i -= size) {
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for (r = i; r * 2 + size < n; r = c) {
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c = r * 2 + size;
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if (c < n - size &&
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cmp_func(base + c, base + c + size) < 0)
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c += size;
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if (cmp_func(base + r, base + c) >= 0)
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break;
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swap_func(base + r, base + c, size);
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}
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}
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/* sort */
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for (i = n - size; i > 0; i -= size) {
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swap_func(base, base + i, size);
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for (r = 0; r * 2 + size < i; r = c) {
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c = r * 2 + size;
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if (c < i - size &&
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cmp_func(base + c, base + c + size) < 0)
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c += size;
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if (cmp_func(base + r, base + c) >= 0)
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break;
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swap_func(base + r, base + c, size);
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}
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}
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}
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EXPORT_SYMBOL(sort);
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