76 lines
2.8 KiB
C
76 lines
2.8 KiB
C
/*
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* Copyright (C) 2008 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <string.h>
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void *memmove(void *dst, const void *src, size_t n)
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{
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const char *p = src;
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char *q = dst;
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/* We can use the optimized memcpy if the destination is below the
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* source (i.e. q < p), or if it is completely over it (i.e. q >= p+n).
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*/
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if (__builtin_expect((q < p) || ((size_t)(q - p) >= n), 1)) {
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return memcpy(dst, src, n);
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} else {
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#define PRELOAD_DISTANCE 64
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/* a semi-optimized memmove(). we're preloading the src and dst buffers
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* as we go */
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size_t c0, c1, i;
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p += n;
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q += n;
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/* note: we preload the destination as well, because the 1-byte at a time
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* copy below doesn't take advantage of the write-buffer, we need
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* to use the cache instead as a poor man's write-combiner */
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__builtin_prefetch(p-1);
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__builtin_prefetch(q-1);
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if (PRELOAD_DISTANCE > 32) {
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__builtin_prefetch(p-(32+1));
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__builtin_prefetch(q-(32+1));
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}
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/* do the prefetech as soon as possible, prevent the compiler to
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* reorder the instructions above the prefetch */
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asm volatile("":::"memory");
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c0 = n & 0x1F; /* cache-line is 32 bytes */
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c1 = n >> 5;
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while ( c1-- ) {
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/* ARMv6 can have up to 3 memory access outstanding */
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__builtin_prefetch(p - (PRELOAD_DISTANCE+1));
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__builtin_prefetch(q - (PRELOAD_DISTANCE+1));
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asm volatile("":::"memory");
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for (i=0 ; i<32 ; i++) {
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*--q = *--p;
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}
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}
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while ( c0-- ) {
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*--q = *--p;
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}
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}
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return dst;
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}
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