private void char2byte(int radix, int fromPos) {
    for (int i = fromPos; i < value.length; i++) {
      value[i] = (byte) Character.digit(value[i], radix);
    }
  }
Convert the chars in value[] to the corresponding integers. Convert invalid
characters to -1.

@param radix
         must be between MIN_RADIX and MAX_RADIX
@param fromPos
         is the first nonzero element
ql/src/java/org/apache/hadoop/hive/ql/udf/UDFConv.java