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
/*
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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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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/sort.h>
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#include <linux/slab.h>
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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 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: pointer to comparison function
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* @swap: 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 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)(const void *, const void *),
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void (*swap)(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)
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swap = (size == 4 ? u32_swap : generic_swap);
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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 && cmp(base + c, base + c + size) < 0)
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c += size;
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if (cmp(base + r, base + c) >= 0)
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break;
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swap(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(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 && cmp(base + c, base + c + size) < 0)
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c += size;
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if (cmp(base + r, base + c) >= 0)
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break;
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swap(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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#if 0
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/* a simple boot-time regression test */
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int cmpint(const void *a, const void *b)
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{
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return *(int *)a - *(int *)b;
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}
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static int sort_test(void)
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{
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int *a, i, r = 1;
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a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
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BUG_ON(!a);
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printk("testing sort()\n");
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for (i = 0; i < 1000; i++) {
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r = (r * 725861) % 6599;
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a[i] = r;
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}
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sort(a, 1000, sizeof(int), cmpint, NULL);
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for (i = 0; i < 999; i++)
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if (a[i] > a[i+1]) {
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printk("sort() failed!\n");
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break;
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}
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kfree(a);
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return 0;
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}
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module_init(sort_test);
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#endif
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