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// SPDX-License-Identifier: GPL-2.0
/*
* A fast, small, non-recursive O(nlog n) sort for the Linux kernel
*
* Jan 23 2005 Matt Mackall <mpm@selenic.com>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/types.h>
#include <linux/export.h>
#include <linux/sort.h>
/**
* is_aligned - is this pointer & size okay for word-wide copying?
* @base: pointer to data
* @size: size of each element
* @align: required aignment (typically 4 or 8)
*
* Returns true if elements can be copied using word loads and stores.
* The size must be a multiple of the alignment, and the base address must
* be if we do not have CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
*
* For some reason, gcc doesn't know to optimize "if (a & mask || b & mask)"
* to "if ((a | b) & mask)", so we do that by hand.
*/
__attribute_const__ __always_inline
static bool is_aligned(const void *base, size_t size, unsigned char align)
{
unsigned char lsbits = (unsigned char)size;
(void)base;
#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
lsbits |= (unsigned char)(uintptr_t)base;
#endif
return (lsbits & (align - 1)) == 0;
}
/**
* swap_words_32 - swap two elements in 32-bit chunks
* @a, @b: pointers to the elements
* @size: element size (must be a multiple of 4)
*
* Exchange the two objects in memory. This exploits base+index addressing,
* which basically all CPUs have, to minimize loop overhead computations.
*
* For some reason, on x86 gcc 7.3.0 adds a redundant test of n at the
* bottom of the loop, even though the zero flag is stil valid from the
* subtract (since the intervening mov instructions don't alter the flags).
* Gcc 8.1.0 doesn't have that problem.
*/
static void swap_words_32(void *a, void *b, int size)
{
size_t n = (unsigned int)size;
do {
u32 t = *(u32 *)(a + (n -= 4));
*(u32 *)(a + n) = *(u32 *)(b + n);
*(u32 *)(b + n) = t;
} while (n);
}
/**
* swap_words_64 - swap two elements in 64-bit chunks
* @a, @b: pointers to the elements
* @size: element size (must be a multiple of 8)
*
* Exchange the two objects in memory. This exploits base+index
* addressing, which basically all CPUs have, to minimize loop overhead
* computations.
*
* We'd like to use 64-bit loads if possible. If they're not, emulating
* one requires base+index+4 addressing which x86 has but most other
* processors do not. If CONFIG_64BIT, we definitely have 64-bit loads,
* but it's possible to have 64-bit loads without 64-bit pointers (e.g.
* x32 ABI). Are there any cases the kernel needs to worry about?
*/
static void swap_words_64(void *a, void *b, int size)
{
size_t n = (unsigned int)size;
do {
#ifdef CONFIG_64BIT
u64 t = *(u64 *)(a + (n -= 8));
*(u64 *)(a + n) = *(u64 *)(b + n);
*(u64 *)(b + n) = t;
#else
/* Use two 32-bit transfers to avoid base+index+4 addressing */
u32 t = *(u32 *)(a + (n -= 4));
*(u32 *)(a + n) = *(u32 *)(b + n);
*(u32 *)(b + n) = t;
t = *(u32 *)(a + (n -= 4));
*(u32 *)(a + n) = *(u32 *)(b + n);
*(u32 *)(b + n) = t;
#endif
} while (n);
}
/**
* swap_bytes - swap two elements a byte at a time
* @a, @b: pointers to the elements
* @size: element size
*
* This is the fallback if alignment doesn't allow using larger chunks.
*/
static void swap_bytes(void *a, void *b, int size)
{
size_t n = (unsigned int)size;
do {
char t = ((char *)a)[--n];
((char *)a)[n] = ((char *)b)[n];
((char *)b)[n] = t;
} while (n);
}
/**
* sort - sort an array of elements
* @base: pointer to data to sort
* @num: number of elements
* @size: size of each element
* @cmp_func: pointer to comparison function
* @swap_func: pointer to swap function or NULL
*
* This function does a heapsort on the given array. You may provide
* a swap_func function if you need to do something more than a memory
* copy (e.g. fix up pointers or auxiliary data), but the built-in swap
* isn't usually a bottleneck.
*
* Sorting time is O(n log n) both on average and worst-case. While
* qsort is about 20% faster on average, it suffers from exploitable
* O(n*n) worst-case behavior and extra memory requirements that make
* it less suitable for kernel use.
*/
void sort(void *base, size_t num, size_t size,
int (*cmp_func)(const void *, const void *),
void (*swap_func)(void *, void *, int size))
{
/* pre-scale counters for performance */
int i = (num/2 - 1) * size, n = num * size, c, r;
if (!swap_func) {
if (is_aligned(base, size, 8))
swap_func = swap_words_64;
else if (is_aligned(base, size, 4))
swap_func = swap_words_32;
else
swap_func = swap_bytes;
}
/* heapify */
for ( ; i >= 0; i -= size) {
for (r = i; r * 2 + size < n; r = c) {
c = r * 2 + size;
if (c < n - size &&
cmp_func(base + c, base + c + size) < 0)
c += size;
if (cmp_func(base + r, base + c) >= 0)
break;
swap_func(base + r, base + c, size);
}
}
/* sort */
for (i = n - size; i > 0; i -= size) {
swap_func(base, base + i, size);
for (r = 0; r * 2 + size < i; r = c) {
c = r * 2 + size;
if (c < i - size &&
cmp_func(base + c, base + c + size) < 0)
c += size;
if (cmp_func(base + r, base + c) >= 0)
break;
swap_func(base + r, base + c, size);
}
}
}
EXPORT_SYMBOL(sort);
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