Question

Help me come up with an obfuscated way to multiply a number by 2, accurate to the second decimal.

Ideas:

• use the Russian multiplication technique
• trig / other mathematical identities
• monte carlo methods
• but of course bonus points for CS trickery

edit:

Just remembered that it’s probably more appropriate to think of this in terms of significant figures, not accurate decimal places. So go for 4 matching leading digits.

Answer 1

The following perl one-liner doubles the first command-line argument:

perl -e '$/=$\=shift;map$\+=$//(++$|+$|)**$_,(++$...$=);print'

You may say that using perl is cheating because everything is obfuscated in perl. You would not be entirely wrong.

Here’s a slightly different approach in (unobfuscated) python:

import math
def double(n) :
    if n == 0 :
        return 0
    a = b = n
    for i in range(1,100) :
        a = 2 + 1.0/a
    a = a - 1
    for i in range(1,100) :
        b = a * b
        a = math.sqrt(a)
    return b