from typing import Optional


def bytes_to_long(buffer: bytes, buffer_size: Optional[int] = None) -> int:
    if buffer_size is not None:
        assert len(buffer) == buffer_size

    num = 0
    for byte in buffer:
        num = num * 256 + byte
    return num


def long_to_bytes(num: int, buffer_size: int) -> bytes:
    assert 0 <= num

    buffer = [0] * buffer_size

    for i in range(buffer_size):
        buffer[-i - 1] = num & 255
        num >>= 8

    return bytes(buffer)