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Message-ID: <20070306183426.10768.51800.stgit@warthog.cambridge.redhat.com>
Date: Tue, 06 Mar 2007 18:34:26 +0000
From: David Howells <dhowells@...hat.com>
To: torvalds@...l.org, akpm@...l.org, benh@...nel.crashing.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com,
johannes@...solutions.net, dhowells@...hat.com
Subject: [PATCH] Fix get_order() [try #2]
From: David Howells <dhowells@...hat.com>
Provide an ilog2_up() that rounds its result up (ilog2() rounds down).
Fix get_order() to use ilog2_up() not ilog2() to get the correct rounding.
Adjust the documentation surrounding ilog2() and co. to indicate what rounding
they perform.
Fix roundup_pow_of_two(1) to give 1, not 0.
Signed-Off-By: David Howells <dhowells@...hat.com>
---
include/asm-generic/page.h | 14 +++++++++-----
include/linux/log2.h | 20 ++++++++++++++++++--
2 files changed, 27 insertions(+), 7 deletions(-)
diff --git a/include/asm-generic/page.h b/include/asm-generic/page.h
index b55052c..c79dc23 100644
--- a/include/asm-generic/page.h
+++ b/include/asm-generic/page.h
@@ -17,11 +17,15 @@ static inline __attribute__((const))
int __get_order(unsigned long size, int page_shift)
{
#if BITS_PER_LONG == 32 && defined(ARCH_HAS_ILOG2_U32)
- int order = __ilog2_u32(size) - page_shift;
- return order >= 0 ? order : 0;
+ if (size <= (1UL << page_shift))
+ return 0;
+ else
+ return __ilog2_u32(size - 1) + 1 - page_shift;
#elif BITS_PER_LONG == 64 && defined(ARCH_HAS_ILOG2_U64)
- int order = __ilog2_u64(size) - page_shift;
- return order >= 0 ? order : 0;
+ if (size <= (1UL << page_shift))
+ return 0;
+ else
+ return __ilog2_u64(size - 1) + 1 - page_shift;
#else
int order;
@@ -46,7 +50,7 @@ int __get_order(unsigned long size, int page_shift)
#define get_order(n) \
( \
__builtin_constant_p(n) ? \
- ((n < (1UL << PAGE_SHIFT)) ? 0 : ilog2(n) - PAGE_SHIFT) : \
+ ((n < (1UL << PAGE_SHIFT)) ? 0 : ilog2_up(n) - PAGE_SHIFT) : \
__get_order(n, PAGE_SHIFT) \
)
diff --git a/include/linux/log2.h b/include/linux/log2.h
index 57e641e..bc3a0eb 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -70,6 +70,8 @@ unsigned long __roundup_pow_of_two(unsigned long n)
* constant-capable log of base 2 calculation
* - this can be used to initialise global variables from constant data, hence
* the massive ternary operator construction
+ * - the result is rounded down
+ * - the result is undefined when n < 1
*
* selects the appropriately-sized optimised version depending on sizeof(n)
*/
@@ -149,6 +151,20 @@ unsigned long __roundup_pow_of_two(unsigned long n)
)
/**
+ * ilog2_up - rounded up log of base 2 of 32-bit or a 64-bit unsigned value
+ * @n - parameter
+ *
+ * constant-capable log of base 2 calculation
+ * - this can be used to initialise global variables from constant data, hence
+ * the massive ternary operator construction
+ * - the result is rounded up
+ * - the result is undefined when n < 1
+ *
+ * selects the appropriately-sized optimised version depending on sizeof(n)
+ */
+#define ilog2_up(n) ((n) == 1 ? 0 : ilog2((n) - 1) + 1)
+
+/**
* roundup_pow_of_two - round the given value up to nearest power of two
* @n - parameter
*
@@ -159,8 +175,8 @@ unsigned long __roundup_pow_of_two(unsigned long n)
#define roundup_pow_of_two(n) \
( \
__builtin_constant_p(n) ? ( \
- (n == 1) ? 0 : \
- (1UL << (ilog2((n) - 1) + 1)) \
+ (n == 1) ? 1 : \
+ (1UL << ilog2_up(n)) \
) : \
__roundup_pow_of_two(n) \
)
-
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