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Diffstat (limited to 'sysdeps/generic/pagecopy.h')
| -rw-r--r-- | sysdeps/generic/pagecopy.h | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/sysdeps/generic/pagecopy.h b/sysdeps/generic/pagecopy.h new file mode 100644 index 0000000000..07202a3119 --- /dev/null +++ b/sysdeps/generic/pagecopy.h @@ -0,0 +1,74 @@ +/* Macros for copying by pages; used in memcpy, memmove. Generic macros. +Copyright (C) 1995 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 Library General Public License as +published by the Free Software Foundation; either version 2 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 +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, 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 + +#define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) \ + do \ + { \ + if ((nbytes) >= PAGE_COPY_THRESHOLD && \ + PAGE_OFFSET (dstp) == PAGE_OFFSET (srcp)) \ + { \ + /* 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 (PAGE_SIZE - 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); \ + nbytes_before -= nbytes_left; \ + nbytes -= nbytes_before; \ + } \ + if (nbytes_before == 0) \ + 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 |