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/* Macros for copying by pages; used in memcpy, memmove. Generic macros.
Copyright (C) 1995, 1997 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
/* This file defines the macro:
PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes)
which is invoked like WORD_COPY_FWD et al. The pointers should be at
least word aligned. This will check if virtual copying by pages can and
should be done and do it if so.
System-specific pagecopy.h files should define these macros and then
#include this file:
PAGE_COPY_THRESHOLD
-- Minimum size for which virtual copying by pages is worthwhile.
PAGE_SIZE
-- Size of a page.
PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes)
-- Macro to perform the virtual copy operation.
The pointers will be aligned to PAGE_SIZE bytes.
*/
#if defined PAGE_COPY_THRESHOLD && PAGE_COPY_THRESHOLD
#include <assert.h>
#define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) \
do \
{ \
if ((nbytes) >= PAGE_COPY_THRESHOLD && \
PAGE_OFFSET ((dstp) - (srcp)) == 0) \
{ \
/* The amount to copy is past the threshold for copying \
pages virtually with kernel VM operations, and the \
source and destination addresses have the same alignment. */ \
size_t nbytes_before = PAGE_OFFSET (-(dstp)); \
if (nbytes_before != 0) \
{ \
/* First copy the words before the first page boundary. */ \
WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before); \
assert (nbytes_left == 0); \
nbytes -= nbytes_before; \
} \
PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes); \
} \
} while (0)
/* The page size is always a power of two, so we can avoid modulo division. */
#define PAGE_OFFSET(n) ((n) & (PAGE_SIZE - 1))
#else
#define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */
#endif
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