From 976a68a20d366e6497253bad9fe0d7a8e42a611c Mon Sep 17 00:00:00 2001 From: Patrick Delaunay 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 --- 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;