Hello,
Am 23.05.2011 11:03, schrieb Matthias Weisser:
In some cases (e.g. bootm with a elf payload which is already at the right position) there is a in place copy of data to the same address. Catching this saves some ms while booting.
Signed-off-by: Matthias Weisserweisserm@arcor.de
Changes since V1:
- Made subject more informative
- Removed the optimization from bcopy as bcopy is not used anywhere
lib/string.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/lib/string.c b/lib/string.c index b375b81..2c4f0ec 100644 --- a/lib/string.c +++ b/lib/string.c @@ -467,6 +467,9 @@ void * memcpy(void *dest, const void *src, size_t count) unsigned long *dl = (unsigned long *)dest, *sl = (unsigned long *)src; char *d8, *s8;
- if (src == dest)
return dest;
here is the same, as in the patch I've commented before. There exist no reason to add a check for identity to memcpy() because memcpy doesn't support overlapping regions (and identity is just a special case of overlapping regions). If something might call memcpy() with overlapping or identical regions, it should use memmove().
/* while all data is aligned (common case), copy a word at a time */ if ( (((ulong)dest | (ulong)src)& (sizeof(*dl) - 1)) == 0) { while (count>= sizeof(*dl)) { @@ -497,6 +500,9 @@ void * memmove(void * dest,const void *src,size_t count) { char *tmp, *s;
- if (src == dest)
return dest;- if (dest<= src) {
Here it is ok, but the check <= could be modified to < too.
Just to clarify my reasoning: the only reason why memcpy() exists, is because it should have been a faster version of memmove() without the necessary checks. So if a bug proof of version of memcpy() is wanted, there is no need to have a different implementation for memcpy() and memcpy() could just be an alias for memmove(). But adding a check for identity to memcpy() is unnecessary.
Sorry, but I had to comment this after having read to many comments in a bug about something similiar in
https://bugzilla.redhat.com/show_bug.cgi?id=638477
(Be aware, reading that bug might hurt your brain)
Regards,
Alexander