#!/usr/bin/python3
# mari von steinkirch @2013
# steinkirch at gmail

''' Clear a bit in a binary number. It is almost like the reverse of set bit:
    1) first create a number filled of 1s, with 0 at i (can create 0001000 and ~)
    2) AND the number so it clears the ith bit
        
    >>> num = int('10010000', 2)
    >>> clear_bit(num, 4)   
    '0b10000000'
    >>> num = int('10010011', 2)
    >>> clear_all_bits_from_i_to_0(num, 2)  
    '0b10010000'
    >>> num = int('1110011', 2)
    >>> clear_all_bits_from_most_sig_to_1(num, 2)  
    '0b11'
'''



def clear_bit(num, i):
    mask = ~ (1 << i)   # -0b10001
    return bin(num & mask)


def clear_all_bits_from_i_to_0(num, i):
    mask = ~ ( (1 << (i+1)) - 1)   
    return bin(num & mask)    


def clear_all_bits_from_most_sig_to_1(num, i):
    mask =  ( 1 << i) -1
    return bin(num & mask)       
    

if __name__ == '__main__':
    import doctest
    doctest.testmod()