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