1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in
12 * the documentation and/or other materials provided with the
13 * distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28 #include <string.h>
29
memmove(void * dst,const void * src,size_t n)30 void *memmove(void *dst, const void *src, size_t n)
31 {
32 const char *p = src;
33 char *q = dst;
34 if (__builtin_expect(q < p, 1)) {
35 return memcpy(dst, src, n);
36 } else {
37 #define PRELOAD_DISTANCE 64
38 /* a semi-optimized memmove(). we're preloading the src and dst buffers
39 * as we go */
40 size_t c0, c1, i;
41 p += n;
42 q += n;
43 /* note: we preload the destination as well, because the 1-byte at a time
44 * copy below doesn't take advantage of the write-buffer, we need
45 * to use the cache instead as a poor man's write-combiner */
46 __builtin_prefetch(p-1);
47 __builtin_prefetch(q-1);
48 if (PRELOAD_DISTANCE > 32) {
49 __builtin_prefetch(p-(32+1));
50 __builtin_prefetch(q-(32+1));
51 }
52 /* do the prefetech as soon as possible, prevent the compiler to
53 * reorder the instructions above the prefetch */
54 asm volatile("":::"memory");
55 c0 = n & 0x1F; /* cache-line is 32 bytes */
56 c1 = n >> 5;
57 while ( c1-- ) {
58 /* ARMv6 can have up to 3 memory access outstanding */
59 __builtin_prefetch(p - (PRELOAD_DISTANCE+1));
60 __builtin_prefetch(q - (PRELOAD_DISTANCE+1));
61 asm volatile("":::"memory");
62 for (i=0 ; i<32 ; i++) {
63 *--q = *--p;
64 }
65 }
66 while ( c0-- ) {
67 *--q = *--p;
68 }
69 }
70
71 return dst;
72 }
73