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lib/sort.c
2.54 KB
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/* * 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> |
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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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{ u32 t = *(u32 *)a; *(u32 *)a = *(u32 *)b; *(u32 *)b = t; } |
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static void generic_swap(void *a, void *b, int size) |
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{ char t; do { t = *(char *)a; *(char *)a++ = *(char *)b; *(char *)b++ = t; } while (--size > 0); } |
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/** |
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* sort - sort an array of elements * @base: pointer to data to sort * @num: number of elements * @size: size of each element |
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* @cmp_func: pointer to comparison function * @swap_func: pointer to swap function or NULL |
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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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* * 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, |
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int (*cmp_func)(const void *, const void *), void (*swap_func)(void *, void *, int size)) |
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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) swap_func = (size == 4 ? u32_swap : generic_swap); |
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/* heapify */ for ( ; i >= 0; i -= size) { |
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for (r = i; r * 2 + size < n; r = c) { c = r * 2 + size; |
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if (c < n - size && 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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} } /* 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) { c = r * 2 + size; |
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if (c < i - size && 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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} } } 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) { |
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int *a, i, r = 1; |
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a = kmalloc(1000 * sizeof(int), GFP_KERNEL); BUG_ON(!a); printk("testing sort() "); 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! "); break; } kfree(a); return 0; } module_init(sort_test); #endif |