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Diffstat (limited to 'libc/string/generic/pagecopy.h')
| -rw-r--r-- | libc/string/generic/pagecopy.h | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/libc/string/generic/pagecopy.h b/libc/string/generic/pagecopy.h new file mode 100644 index 000000000..5a0ada1fa --- /dev/null +++ b/libc/string/generic/pagecopy.h @@ -0,0 +1,75 @@ +/* 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 |