# retoor <retoor@molodetz.nl>

from typing import Sequence


def add(left: int, right: int) -> int:
    return left + right


def subtract(left: int, right: int) -> int:
    return left - right


def clamp(value: int, low: int, high: int) -> int:
    if low > high:
        raise ValueError
    if value < low:
        return low
    if value > high:
        return high
    return value


def clamp_to_byte(value: int) -> int:
    return max(0, min(255, value))


def variance(values: Sequence[float]) -> float:
    if not values:
        raise ValueError
    mean = sum(values) / len(values)
    return sum((x - mean) ** 2 for x in values) / len(values)