def mmap_move(fileobj, dest, src, count):
    """Mmaps the file object if possible and moves 'count' data
    from 'src' to 'dest'. All data has to be inside the file size
    (enlarging the file through this function isn't possible)

    Will adjust the file offset.

    Args:
        fileobj (fileobj)
        dest (int): The destination offset
        src (int): The source offset
        count (int) The amount of data to move
    Raises:
        mmap.error: In case move failed
        IOError: In case an operation on the fileobj fails
        ValueError: In case invalid parameters were given
    """

    assert mmap is not None, "no mmap support"

    if dest < 0 or src < 0 or count < 0:
        raise ValueError("Invalid parameters")

    try:
        fileno = fileobj.fileno()
    except (AttributeError, IOError):
        raise mmap.error(
            "File object does not expose/support a file descriptor")

    fileobj.seek(0, 2)
    filesize = fileobj.tell()
    length = max(dest, src) + count

    if length > filesize:
        raise ValueError("Not in file size boundary")

    offset = ((min(dest, src) // mmap.ALLOCATIONGRANULARITY) *
              mmap.ALLOCATIONGRANULARITY)
    assert dest >= offset
    assert src >= offset
    assert offset % mmap.ALLOCATIONGRANULARITY == 0

    # Windows doesn't handle empty mappings, add a fast path here instead
    if count == 0:
        return

    # fast path
    if src == dest:
        return

    fileobj.flush()
    file_map = mmap.mmap(fileno, length - offset, offset=offset)
    try:
        file_map.move(dest - offset, src - offset, count)
    finally:
        file_map.close()