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lib/string: optimized memmove

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When the destination buffer is before the source one, or when the buffers
doesn't overlap, it's safe to use memcpy() instead, which is optimized to
use a bigger data size possible.

This "optimization" only covers a common case.  In future, proper code
which does the same thing as memcpy() does but backwards can be done.

Link: https://lkml.kernel.org/r/20210702123153.14093-3-mcroce@linux.microsoft.com
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Laight <David.Laight@aculab.com>
Cc: Drew Fustini <drew@beagleboard.org>
Cc: Emil Renner Berthing <kernel@esmil.dk>
Cc: Guo Ren <guoren@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nick Kossifidis <mick@ics.forth.gr>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jebaitedneko <Jebaitedneko@gmail.com>
Signed-off-by: celtare21 <celtare21@gmail.com>
This commit is contained in:
Matteo Croce 2021-07-16 19:26:31 +05:30 committed by Ksawlii
parent e4f231582a
commit 95dce0e9be
1 changed files with 6 additions and 12 deletions
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18
lib/string.c
View file

@ -932,19 +932,13 @@ EXPORT_SYMBOL(memcpy);
*/
void *memmove(void *dest, const void *src, size_t count)
{
char *tmp;
const char *s;
if (dest < src || src + count <= dest)
return memcpy(dest, src, count);
if (dest > src) {
const char *s = src + count;
char *tmp = dest + count;
if (dest <= src) {
tmp = dest;
s = src;
while (count--)
*tmp++ = *s++;
} else {
tmp = dest;
tmp += count;
s = src;
s += count;
while (count--)
*--tmp = *--s;
}