winmmap.h

#include <io.h>
#include <errno.h>
#include <windows.h>
#include <sys/types.h>

#define PROT_NONE       0x00
#define PROT_READ       0x01
#define PROT_WRITE      0x02
#define PROT_EXEC       0x04

#define MAP_FILE        0x00
#define MAP_SHARED      0x01
#define MAP_PRIVATE     0x02
#define MAP_FIXED       0x10
#define MAP_TYPE        0x0F
#define MAP_ANON   0x20
#define MAP_FAILED      ((void*) -1)

#define MS_ASYNC        0x01
#define MS_SYNC         0x02
#define MS_INVALIDATE   0x04

#define MADV_NORMAL     0x00
#define MADV_RANDOM     0x01
#define MADV_SEQUENTIAL 0x02
#define MADV_WILLNEED   0x03
#define MADV_DONTNEED   0x04

inline void* mmap(void* addr, size_t length, int prot, int flags, int fd, size_t offset) {
    if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC))
        return MAP_FAILED;
    if (fd == -1) {
        if (!(flags & MAP_ANON) || offset)
            return MAP_FAILED;
    } else if (flags & MAP_ANON)
        return MAP_FAILED;

    DWORD protect;
    if (prot & PROT_WRITE) {
        if (prot & PROT_EXEC)
            protect = PAGE_EXECUTE_READWRITE;
        else
            protect = PAGE_READWRITE;
    } else if (prot & PROT_EXEC) {
        if (prot & PROT_READ)
            protect = PAGE_EXECUTE_READ;
        else
            protect = PAGE_EXECUTE;
    } else
        protect = PAGE_READONLY;

    size_t end = length + offset;
    const DWORD dwEndLow = (sizeof(size_t) > sizeof(DWORD)) ? DWORD(end & 0x0000FFFFL) : DWORD(end);
    const DWORD dwEndHigh = (sizeof(size_t) > sizeof(DWORD)) ? DWORD(end>>16) : DWORD(0);
    const DWORD dwOffsetLow = (sizeof(size_t) > sizeof(DWORD)) ? DWORD(offset & 0x0000FFFFL) : DWORD(offset);
    const DWORD dwOffsetHigh = (sizeof(size_t) > sizeof(DWORD)) ? DWORD(offset>>16) : DWORD(0);

    HANDLE h = (fd != -1) ? HANDLE(_get_osfhandle(fd)) : INVALID_HANDLE_VALUE;
    HANDLE fm = CreateFileMapping(h, nullptr, protect, dwEndHigh, dwEndLow, nullptr);
    if (fm == nullptr)
        return MAP_FAILED;

    DWORD dwDesiredAccess;
    if (prot & PROT_WRITE)
        dwDesiredAccess = FILE_MAP_WRITE;
    else
        dwDesiredAccess = FILE_MAP_READ;
    if (prot & PROT_EXEC)
        dwDesiredAccess |= FILE_MAP_EXECUTE;
    if (flags & MAP_PRIVATE)
        dwDesiredAccess |= FILE_MAP_COPY;

    void* map = MapViewOfFile(fm, dwDesiredAccess, dwOffsetHigh, dwOffsetLow, length);
    CloseHandle(fm);

    return (map != nullptr) ? map : MAP_FAILED;
}

inline int munmap(void* addr, size_t length) {
    if (UnmapViewOfFile(addr))
        return 0;

    errno = GetLastError();
    return -1;
}

inline int msync(void* addr, size_t length, int flags) {
    if (FlushViewOfFile(addr, length))
        return 0;

    errno = GetLastError();
    return -1;
}

inline int madvise(void* addr, size_t length, int advice) {
    return 0;   // Unsupported on Windows
}