/* 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