4bdcfb1541
git-subtree-dir: external/mio git-subtree-split: 8b6b7d878c89e81614d05edca7936de41ccdd2da
79 lines
2.5 KiB
C++
79 lines
2.5 KiB
C++
/* Copyright 2017 https://github.com/mandreyel
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this
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* software and associated documentation files (the "Software"), to deal in the Software
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* without restriction, including without limitation the rights to use, copy, modify,
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* merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to the following
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* conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies
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* or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
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* PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
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* CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
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* OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#ifndef MIO_PAGE_HEADER
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#define MIO_PAGE_HEADER
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#ifdef _WIN32
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# include <windows.h>
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#else
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# include <unistd.h>
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#endif
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namespace mio {
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/**
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* This is used by `basic_mmap` to determine whether to create a read-only or
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* a read-write memory mapping.
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*/
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enum class access_mode
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{
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read,
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write
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};
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/**
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* Determines the operating system's page allocation granularity.
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*
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* On the first call to this function, it invokes the operating system specific syscall
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* to determine the page size, caches the value, and returns it. Any subsequent call to
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* this function serves the cached value, so no further syscalls are made.
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*/
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inline size_t page_size()
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{
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static const size_t page_size = []
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{
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#ifdef _WIN32
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SYSTEM_INFO SystemInfo;
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GetSystemInfo(&SystemInfo);
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return SystemInfo.dwAllocationGranularity;
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#else
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return sysconf(_SC_PAGE_SIZE);
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#endif
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}();
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return page_size;
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}
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/**
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* Alligns `offset` to the operating's system page size such that it subtracts the
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* difference until the nearest page boundary before `offset`, or does nothing if
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* `offset` is already page aligned.
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*/
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inline size_t make_offset_page_aligned(size_t offset) noexcept
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{
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const size_t page_size_ = page_size();
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// Use integer division to round down to the nearest page alignment.
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return offset / page_size_ * page_size_;
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}
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} // namespace mio
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#endif // MIO_PAGE_HEADER
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