IEEE 754 (double precision) decode practice.

ieee754.rb

def ieee754_double(num)
  int64 = [num].pack("d").unpack("Q")[0]

  sign = (int64 & (1 << 63)) == 0 ? 1 : -1
  exp =  (int64 & 0x7ff0000000000000) >> 52
  frac = (int64 & 0x000fffffffffffff)

  if exp == 0 and frac == 0
    return sign * 0.0
  end
  if exp == 0x7ff
    if frac == 0
      # +Infinity/-Infinity
      return sign * (1.0 / 0.0)
    else
      # NaN
      return (0.0 / 0.0)
    end
  end

  if exp != 0
    # regular number
    exp -= 0x3ff
    frac += 0x0010000000000000
  else
    # non regular number
    exp -= 0x3fe
  end
  return sign * (frac * (2.0 ** -52)) * (2.0 ** exp)
end