private static long readLongBits(JsonIterator iter) throws IOException {
        Slice slice = iter.readStringAsSlice();
        byte[] data = slice.data();
        long val = 0;
        for (int i = slice.head(); i < slice.tail(); i++) {
            byte b = data[i];
            val = val << 4 | DEC[b];
        }
        return val;
    }
encode float/double as base64, faster than PreciseFloatSupport
src/main/java/com/jsoniter/extra/Base64FloatSupport.java