| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | /* Macros for copying by pages; used in memcpy, memmove. Generic macros. |
| 2 | Copyright (C) 1995, 1997 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | |
| 5 | The GNU C Library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public |
| 7 | License as published by the Free Software Foundation; either |
| 8 | version 2.1 of the License, or (at your option) any later version. |
| 9 | |
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 13 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with the GNU C Library; if not, write to the Free |
| 17 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 18 | 02111-1307 USA. */ |
| 19 | |
| 20 | /* This file defines the macro: |
| 21 | |
| 22 | PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes) |
| 23 | |
| 24 | which is invoked like WORD_COPY_FWD et al. The pointers should be at |
| 25 | least word aligned. This will check if virtual copying by pages can and |
| 26 | should be done and do it if so. |
| 27 | |
| 28 | System-specific pagecopy.h files should define these macros and then |
| 29 | #include this file: |
| 30 | |
| 31 | PAGE_COPY_THRESHOLD |
| 32 | -- Minimum size for which virtual copying by pages is worthwhile. |
| 33 | |
| 34 | PAGE_SIZE |
| 35 | -- Size of a page. |
| 36 | |
| 37 | PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes) |
| 38 | -- Macro to perform the virtual copy operation. |
| 39 | The pointers will be aligned to PAGE_SIZE bytes. |
| 40 | */ |
| 41 | |
| 42 | |
| 43 | #if defined PAGE_COPY_THRESHOLD && PAGE_COPY_THRESHOLD |
| 44 | |
| 45 | #include <assert.h> |
| 46 | |
| 47 | #define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) \ |
| 48 | do \ |
| 49 | { \ |
| 50 | if ((nbytes) >= PAGE_COPY_THRESHOLD && \ |
| 51 | PAGE_OFFSET ((dstp) - (srcp)) == 0) \ |
| 52 | { \ |
| 53 | /* The amount to copy is past the threshold for copying \ |
| 54 | pages virtually with kernel VM operations, and the \ |
| 55 | source and destination addresses have the same alignment. */ \ |
| 56 | size_t nbytes_before = PAGE_OFFSET (-(dstp)); \ |
| 57 | if (nbytes_before != 0) \ |
| 58 | { \ |
| 59 | /* First copy the words before the first page boundary. */ \ |
| 60 | WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before); \ |
| 61 | assert (nbytes_left == 0); \ |
| 62 | nbytes -= nbytes_before; \ |
| 63 | } \ |
| 64 | PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes); \ |
| 65 | } \ |
| 66 | } while (0) |
| 67 | |
| 68 | /* The page size is always a power of two, so we can avoid modulo division. */ |
| 69 | #define PAGE_OFFSET(n) ((n) & (PAGE_SIZE - 1)) |
| 70 | |
| 71 | #else |
| 72 | |
| 73 | #define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */ |
| 74 | |
| 75 | #endif |