linux-kernel - [PATCH] lib/sort: Move the alignment check into a function

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Message-Id: <1431942609-14457-1-git-send-email-daniel.wagner@bmw-carit.de>
Date:	Mon, 18 May 2015 11:50:09 +0200
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Wagner <daniel.wagner@...-carit.de>
Subject: [PATCH] lib/sort: Move the alignment check into a function

Rasmus Villemoes suggestes to move the aliment check into a separate
function in order to improve the readability.

Furthermore, let's avoid the switch statement since gcc might mess it
up. My gcc 4.9.2 produces the same code for the x86_64
configuration. That is

	switch (size) {
		case 4:
			if (alignment_ok(base, 4))
				swap_func = u32_swap;
			       break;
		case 8:
			if (alignment_ok(base, 8))
				swap_func = u64_swap;
			break;
		}
		if (!swap_func)
			swap_func = generic_swap;
	}

resulted into the same object code.

Link: https://lkml.org/lkml/2015/5/15/89
Signed-off-by: Daniel Wagner <daniel.wagner@...-carit.de>
Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Andrew Morton <akpm@...ux-foundation.org>

--

Hi,

I did this patch on top of current mmotm tree [1]. Hopefully I got
this right, if you want it merged into v2 of this patch or any
different version just let me know. Eventually I will get this right
:)

cheers,
daniel

[1] http://ozlabs.org/~akpm/mmotm/
---
 lib/sort.c | 30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

diff --git a/lib/sort.c b/lib/sort.c
index 9c6b229..fc20df4 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -8,6 +8,12 @@
 #include <linux/export.h>
 #include <linux/sort.h>
 
+static int alignment_ok(const void *base, int align)
+{
+	return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
+		((unsigned long)base & (align - 1)) == 0;
+}
+
 static void u32_swap(void *a, void *b, int size)
 {
 	u32 t = *(u32 *)a;
@@ -58,29 +64,11 @@ void sort(void *base, size_t num, size_t size,
 	int i = (num/2 - 1) * size, n = num * size, c, r;
 
 	if (!swap_func) {
-#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
-		switch (size) {
-		case 4:
+		if (size == 4 && alignment_ok(base, 4))
 			swap_func = u32_swap;
-			break;
-		case 8:
+		else if (size == 8 && alignment_ok(base, 8))
 			swap_func = u64_swap;
-			break;
-		}
-#else
-		switch (size) {
-		case 4:
-			if (((unsigned long)base & 3) == 0)
-				swap_func = u32_swap;
-			break;
-		case 8:
-			if (((unsigned long)base & 7) == 0)
-				swap_func = u64_swap;
-			break;
-		}
-#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
-
-		if (!swap_func)
+		else
 			swap_func = generic_swap;
 	}
 
-- 
2.1.0

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