#
# Lab 5: Tasks 2 and 3
#

def bitwise_or(b1, b2):
    """ computes and returns the bitwise OR of binary numbers b1 and b2
        inputs: b1 and b2 are strings that represent binary numbers
    """
    if b1 == '' and b2 == '':    # not strictly needed
        return ''
    elif b1 == '':
        return b2
    elif b2 == '':
        return b1
    else:
        or_rest = bitwise_or(b1[:-1], b2[:-1])
        if b1[-1] == '1' or b2[-1] == '1':
            return or_rest + '1'
        else:
            return or_rest + '0'

def left_shift(b, n):
    """  returns the result of performing a left shift of 
         the bitstring b by n places
    """
    if n <= 0:
        return b
    else:
        return b + ('0' * n)
    
def right_shift(b, n):
    """  returns the result of performing a right shift of 
         the bitstring b by n places
    """
    if n <= 0:
        return b    
    elif n >= len(b):
        return '0'
    else:
        return b[:-n]