hex2bin.rb

MAP = {
  '0' => '0000',
  '1' => '0001',
  '2' => '0010',
  '3' => '0011',
  '4' => '0100',
  '5' => '0101',
  '6' => '0110',
  '7' => '0111',
  '8' => '1000',
  '9' => '1001',
  'a' => '1010',
  'b' => '1011',
  'c' => '1100',
  'd' => '1101',
  'e' => '1110',
  'f' => '1111'
}

def hex2bin(hex_string)
  result = ''
  hex_string.chars.each{ |c|
    c = hex2bin_char(c) unless c.match /\s/
    result += c
  }
  result
end

def hex2bin_char(char)
  MAP[char.downcase]
end

Converts a string of "hexidecimal" or "hex" to a sting of "binary". Whitespace passes through to the returned string.