linux-kernel - [PATCH v2] lib: One less subtraction in binary search iterations.

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Date:	Mon,  8 Jul 2013 23:37:02 -0700
From:	Wedson Almeida Filho <wedsonaf@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Joe Perches <joe@...ches.com>
Cc:	Tim Abbott <tabbott@...lice.com>, linux-kernel@...r.kernel.org,
	Wedson Almeida Filho <wedsonaf@...il.com>
Subject: [PATCH v2] lib: One less subtraction in binary search iterations.

The subtraction is removed at the expense of generality: when the element size
is 1, the array length cannot exceed half the architecture's addressable
memory.

Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
---
 lib/bsearch.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/bsearch.c b/lib/bsearch.c
index e33c179..668ae6c 100644
--- a/lib/bsearch.c
+++ b/lib/bsearch.c
@@ -24,6 +24,11 @@
  * contents of the array should already be in ascending sorted order
  * under the provided comparison function.
  *
+ * There is a limitation when @size is 1: in this case @num must be at
+ * most SIZE_MAX / 2; that is, the number of elements in the sorted
+ * array must be at most half the maximum number expressible as a size_t
+ * to avoid overflows.
+ *
  * Note that the key need not have the same type as the elements in
  * the array, e.g. key could be a string and the comparison function
  * could compare the string with the struct's name field.  However, if
@@ -37,7 +42,7 @@ void *bsearch(const void *key, const void *base, size_t num, size_t size,
 	int result;
 
 	while (start < end) {
-		size_t mid = start + (end - start) / 2;
+		size_t mid = (start + end) / 2;
 
 		result = cmp(key, base + mid * size);
 		if (result < 0)
-- 
1.7.9.5

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