mirror of
https://github.com/FEX-Emu/linux.git
synced 2024-12-25 10:59:05 +00:00
995e4286a0
Hello, I fixed and tested a small bug in lib/sort.c file, heap sort function. The fix avoids unnecessary swap of contents when i is 0 (saves few loads and stores), which happens every time sort function is called. I felt the fix is worth bringing it to your attention given the importance and frequent use of the sort function. Acked-by: Matt Mackall <mpm@selenic.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
122 lines
2.5 KiB
C
122 lines
2.5 KiB
C
/*
|
|
* A fast, small, non-recursive O(nlog n) sort for the Linux kernel
|
|
*
|
|
* Jan 23 2005 Matt Mackall <mpm@selenic.com>
|
|
*/
|
|
|
|
#include <linux/kernel.h>
|
|
#include <linux/module.h>
|
|
#include <linux/sort.h>
|
|
#include <linux/slab.h>
|
|
|
|
static void u32_swap(void *a, void *b, int size)
|
|
{
|
|
u32 t = *(u32 *)a;
|
|
*(u32 *)a = *(u32 *)b;
|
|
*(u32 *)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: pointer to comparison function
|
|
* @swap: pointer to swap function or NULL
|
|
*
|
|
* This function does a heapsort on the given array. You may provide a
|
|
* swap 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)(const void *, const void *),
|
|
void (*swap)(void *, void *, int size))
|
|
{
|
|
/* pre-scale counters for performance */
|
|
int i = (num/2 - 1) * size, n = num * size, c, r;
|
|
|
|
if (!swap)
|
|
swap = (size == 4 ? u32_swap : 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(base + c, base + c + size) < 0)
|
|
c += size;
|
|
if (cmp(base + r, base + c) >= 0)
|
|
break;
|
|
swap(base + r, base + c, size);
|
|
}
|
|
}
|
|
|
|
/* sort */
|
|
for (i = n - size; i > 0; i -= size) {
|
|
swap(base, base + i, size);
|
|
for (r = 0; r * 2 + size < i; r = c) {
|
|
c = r * 2 + size;
|
|
if (c < i - size && cmp(base + c, base + c + size) < 0)
|
|
c += size;
|
|
if (cmp(base + r, base + c) >= 0)
|
|
break;
|
|
swap(base + r, base + c, size);
|
|
}
|
|
}
|
|
}
|
|
|
|
EXPORT_SYMBOL(sort);
|
|
|
|
#if 0
|
|
/* a simple boot-time regression test */
|
|
|
|
int cmpint(const void *a, const void *b)
|
|
{
|
|
return *(int *)a - *(int *)b;
|
|
}
|
|
|
|
static int sort_test(void)
|
|
{
|
|
int *a, i, r = 1;
|
|
|
|
a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
|
|
BUG_ON(!a);
|
|
|
|
printk("testing sort()\n");
|
|
|
|
for (i = 0; i < 1000; i++) {
|
|
r = (r * 725861) % 6599;
|
|
a[i] = r;
|
|
}
|
|
|
|
sort(a, 1000, sizeof(int), cmpint, NULL);
|
|
|
|
for (i = 0; i < 999; i++)
|
|
if (a[i] > a[i+1]) {
|
|
printk("sort() failed!\n");
|
|
break;
|
|
}
|
|
|
|
kfree(a);
|
|
|
|
return 0;
|
|
}
|
|
|
|
module_init(sort_test);
|
|
#endif
|