def _gcd(a, b):
    """Computes the greatest common divisor of two numbers using Euclid's Algorithm.
    
    Example:
        >>> _gcd(30, 18)
        6
    
    Args:
        a (int): The first parameter.
        b (int): The second parameter.
        
    Returns:
        int: The greatest common divisor of a and b.
        
    """
    while b:      
        a, b = b, a % b
    return a