/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_PAGE_HEADER
#define MIO_PAGE_HEADER

#ifdef _WIN32
# include <windows.h>
#else
# include <unistd.h>
#endif

namespace mio {

/**
 * This is used by `basic_mmap` to determine whether to create a read-only or
 * a read-write memory mapping.
 */
enum class access_mode
{
    read,
    write
};

/**
 * Determines the operating system's page allocation granularity.
 *
 * On the first call to this function, it invokes the operating system specific syscall
 * to determine the page size, caches the value, and returns it. Any subsequent call to
 * this function serves the cached value, so no further syscalls are made.
 */
inline size_t page_size()
{
    static const size_t page_size = []
    {
#ifdef _WIN32
        SYSTEM_INFO SystemInfo;
        GetSystemInfo(&SystemInfo);
        return SystemInfo.dwAllocationGranularity;
#else
        return sysconf(_SC_PAGE_SIZE);
#endif
    }();
    return page_size;
}

/**
 * Alligns `offset` to the operating's system page size such that it subtracts the
 * difference until the nearest page boundary before `offset`, or does nothing if
 * `offset` is already page aligned.
 */
inline size_t make_offset_page_aligned(size_t offset) noexcept
{
    const size_t page_size_ = page_size();
    // Use integer division to round down to the nearest page alignment.
    return offset / page_size_ * page_size_;
}

} // namespace mio

#endif // MIO_PAGE_HEADER