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Merge "Use more optimized version of memmove"

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David Turner 2011-02-04 05:13:35 -08:00 committed by Android Code Review
commit 2282ecc295
1 changed files with 3 additions and 34 deletions
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37
libc/string/memmove.c
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@ -26,6 +26,7 @@
* SUCH DAMAGE.
*/
#include <string.h>
#include <strings.h>
void *memmove(void *dst, const void *src, size_t n)
{
@ -37,39 +38,7 @@ void *memmove(void *dst, const void *src, size_t n)
if (__builtin_expect((q < p) || ((size_t)(q - p) >= n), 1)) {
return memcpy(dst, src, n);
} else {
#define PRELOAD_DISTANCE 64
/* a semi-optimized memmove(). we're preloading the src and dst buffers
* as we go */
size_t c0, c1, i;
p += n;
q += n;
/* note: we preload the destination as well, because the 1-byte at a time
* copy below doesn't take advantage of the write-buffer, we need
* to use the cache instead as a poor man's write-combiner */
__builtin_prefetch(p-1);
__builtin_prefetch(q-1);
if (PRELOAD_DISTANCE > 32) {
__builtin_prefetch(p-(32+1));
__builtin_prefetch(q-(32+1));
}
/* do the prefetech as soon as possible, prevent the compiler to
* reorder the instructions above the prefetch */
asm volatile("":::"memory");
c0 = n & 0x1F; /* cache-line is 32 bytes */
c1 = n >> 5;
while ( c1-- ) {
/* ARMv6 can have up to 3 memory access outstanding */
__builtin_prefetch(p - (PRELOAD_DISTANCE+1));
__builtin_prefetch(q - (PRELOAD_DISTANCE+1));
asm volatile("":::"memory");
for (i=0 ; i<32 ; i++) {
*--q = *--p;
}
}
while ( c0-- ) {
*--q = *--p;
}
bcopy(src, dst, n);
return dst;
}
return dst;
}