How can I convert a string of binary digits to a number?
I've got this but I imagine there's some kind of 
built-in method. Is there?

def BinStrToNum ( binStr )
  sum = 0
  digit = 1
  binStr.reverse.each_byte { |i|
    sum += (i-48)*digit
    digit <<= 1
  }
  return sum
end

Thanks,
Andrew