linux-kernel - [PATCH] lib: memmove: Use optimised memcpy if possible

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Date:   Wed,  4 Oct 2017 22:26:05 +0530
From:   PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
To:     linux-kernel@...r.kernel.org, dan.carpenter@...cle.com,
        mchehab@...nel.org, paul.burton@...tec.com
Cc:     PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
Subject: [PATCH] lib: memmove: Use optimised memcpy if possible

When there is no overlap between src and dst use optimised memcpy if it
is available.

Signed-off-by: Paul Burton <paul.burton@...tec.com>
Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
---
This change is a small part of a patch [1] from Paul Burton. I have
added his Signed-off by. I do not know whether it is correct. Please let
me know if it has to be changed, I will send a v2.

This patch is boot tested with qemu for MIPS architecture by removing
mips's memmove routine. This patch does not contain MIPS changes. I
will try to find out why [1] was not taken already and figure out what
to do.

1. https://patchwork.linux-mips.org/patch/14517/

 lib/string.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/lib/string.c b/lib/string.c
index 9921dc2..462ab7b 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -825,6 +825,17 @@ void *memmove(void *dest, const void *src, size_t count)
 	char *tmp;
 	const char *s;
 
+#ifdef __HAVE_ARCH_MEMCPY
+	/* Use optimised memcpy when there is no overlap */
+	const char *s_end = src + count;
+	const char *d = dest;
+	char *d_end = dest + count;
+
+	s = src;
+	if ((d_end <= s) || (s_end <= d))
+		return memcpy(dest, src, count);
+#endif /* __HAVE_ARCH_MEMCPY */
+
 	if (dest <= src) {
 		tmp = dest;
 		s = src;
-- 
2.10.0