From 976a68a20d366e6497253bad9fe0d7a8e42a611c Mon Sep 17 00:00:00 2001
From: Patrick Delaunay <patrick.delaunay@foss.st.com>
Date: Fri, 11 Dec 2020 14:59:23 +0100
Subject: [PATCH] string: Use memcpy() within memmove() when we can
A common use of memmove() can be handled by memcpy(). Also memcpy()
includes an optimization for large sizes: it copies a word at a time. So
we can get a speed-up by calling memcpy() to handle our move in this case.
Update memmove() to call also memcpy() if the source don't overlap
the destination (src + count <= dest).
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
---
lib/string.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/lib/string.c b/lib/string.c
index ae7835f600..73b984123d 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -567,7 +567,19 @@ void * memmove(void * dest,const void *src,size_t count)
{
char *tmp, *s;
- if (dest <= src) {
+ if (dest <= src || (src + count) <= dest) {
+ /*
+ * Use the fast memcpy implementation (ARCH optimized or lib/string.c) when it is possible:
+ * - when dest is before src (assuming that memcpy is doing forward-copying)
+ * - when destination don't overlap the source buffer (src + count <= dest)
+ *
+ * WARNING: the first optimisation cause an issue, when __HAVE_ARCH_MEMCPY is defined,
+ * __HAVE_ARCH_MEMMOVE is not defined and if the memcpy ARCH-specific
+ * implementation is not doing a forward-copying.
+ *
+ * No issue today because memcpy is doing a forward-copying in lib/string.c and for ARM32
+ * architecture; no other arches use __HAVE_ARCH_MEMCPY without __HAVE_ARCH_MEMMOVE.
+ */
memcpy(dest, src, count);
} else {
tmp = (char *) dest + count;
--
2.39.5