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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, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+/* 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 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