linux-kernel - [PATCH] low performance of lib/sort.c , kernel 2.6.18

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Message-ID: <76505a370609280818r3ffc9a4akf4cec6ed366d32e3@mail.gmail.com>
Date:	Thu, 28 Sep 2006 23:18:45 +0800
From:	keios <keios.cn@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	"Andrew Morton" <akpm@...l.org>, "Matt Mackall" <mpm@...enic.com>
Subject: [PATCH] low performance of lib/sort.c , kernel 2.6.18

It is a non-standard heap-sort algorithm implementation because the
index of child node is wrong . The sort function still outputs right
result, but the performance is O( n * ( log(n) + 1 ) ) , about 10% ~
20% worse than standard algorithm .

Signed-off-by: keios <keios.cn@...il.com>
-----
diff -Nraup a/lib/sort.c b/lib/sort.c
--- a/lib/sort.c	2006-09-20 11:42:06.000000000 +0800
+++ b/lib/sort.c	2006-09-27 21:26:38.000000000 +0800
@@ -49,15 +49,15 @@ void sort(void *base, size_t num, size_t
 	  void (*swap)(void *, void *, int size))
 {
 	/* pre-scale counters for performance */
-	int i = (num/2) * size, n = num * size, c, r;
+	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 < n; r  = c) {
-			c = r * 2;
+		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)
@@ -69,8 +69,8 @@ void sort(void *base, size_t num, size_t
 	/* sort */
 	for (i = n - size; i >= 0; i -= size) {
 		swap(base, base + i, size);
-		for (r = 0; r * 2 < i; r = c) {
-			c = r * 2;
+		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)
-
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