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string: Use memcpy() within memmove() when we can

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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>
This commit is contained in:
Patrick Delaunay
2020-12-11 14:59:23 +01:00
committed by Tom Rini
parent 67b2ed0243
commit 976a68a20d
1 changed files with 13 additions and 1 deletions
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14
lib/string.c
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@@ -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;