.Int: ClassType
.Int.
    '''
    Number of ones in the binary representation of the absolute value of self.

    Also known as the population count.
    '''
    '''japanese
    2進数表現の絶対値の中の1の数。

    ハミング重みとも呼ばれる。
    '''
    '''erg
    assert bin(13) == "0b1101"
    assert 13.bit_count() == 3
    '''
    bit_count: (self: .Int) -> Nat
    '''
    Number of bits necessary to represent self in binary.
    '''
    '''japanese
    2進数表現においてselfを表すのに必要なビット数。
    '''
    '''erg
    assert bin(37) == "0b100101"
    assert 37.bit_length() == 6
    '''
    bit_length: (self: .Int) -> Nat