code: def _float_to_bits(value, lower=-90.0, middle=0.0, upper=90.0, length=15):
    
    ret = []
    for i in range(length):
      if value >= middle:
        lower = middle
        ret.append(1)
      else:
        upper = middle
        ret.append(0)
      middle = (upper + lower) / 2
    return ret
docs: Convert a float to a list of GeoHash bits.