Permalink
106 lines (92 sloc) 2.44 KB
/*
* 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>
static int alignment_ok(const void *base, int align)
{
return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
((unsigned long)base & (align - 1)) == 0;
}
static void u32_swap(void *a, void *b, int size)
{
u32 t = *(u32 *)a;
*(u32 *)a = *(u32 *)b;
*(u32 *)b = t;
}
static void u64_swap(void *a, void *b, int size)
{
u64 t = *(u64 *)a;
*(u64 *)a = *(u64 *)b;
*(u64 *)b = t;
}
static void generic_swap(void *a, void *b, int size)
{
char t;
do {
t = *(char *)a;
*(char *)a++ = *(char *)b;
*(char *)b++ = t;
} while (--size > 0);
}
/**
* 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 optimized to your element type.
*
* 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 (size == 4 && alignment_ok(base, 4))
swap_func = u32_swap;
else if (size == 8 && alignment_ok(base, 8))
swap_func = u64_swap;
else
swap_func = generic_swap;
}
/* 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);