CODEWITHSUNDEEP
pythonbit-manipulation
yasar
yasar

Reputation: 13758

bitwise rotating whole text

For the fun of it, I am trying to bitwise rotate a whole text to right. Meaning, I want every character's last bit (lsb) end up being next character's first bit (msb) and last character's last bit to be first character's first bit. Here is what I have tried;

def bitwise_text_rotate(text):
    # make a list of ascii codes
    characters = [ord(a) for a in text]

    # save last character's right-most bit
    carry_bit = characters[-1] & 1

    # list of processed characters
    output = []

    for char in characters:
        print "processing", char
        last_bit = char & 1
        char = char >> 1
        mask = (carry_bit << 8) & 1
        char = char & mask
        print "appending", char
        output.append(char)
        carry_bit = last_bit

    return "".join([chr(a) for a in output])

But it doesn't work. I am getting all zeros. Any ideas how I could do this better, or what am I doing wrong here?

Upvotes: 0

Views: 235

Answers (2)

Mark Tolonen
Mark Tolonen

Reputation: 177901

These lines are incorrect:

mask = (carry_bit << 8) & 1
char = char & mask

Use:

mask = carry_bit << 7
char = char | mask

Upvotes: 1

Mark Byers
Mark Byers

Reputation: 838696

Try this:

s = map(ord, text)
return ''.join(chr(((a&1)<<7) + (b>>1)) for a,b in zip(s[-1:] + s, s))

Upvotes: 1

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