code: public static byte[] decodeHexDump(CharSequence hexDump, int fromIndex, int length) {
          if (length < 0 || (length & 1) != 0) {
              throw new IllegalArgumentException("length: " + length);
          }
          if (length == 0) {
              return EmptyArrays.EMPTY_BYTES;
          }
          byte[] bytes = new byte[length >>> 1];
          for (int i = 0; i < length; i += 2) {
              bytes[i >>> 1] = decodeHexByte(hexDump, fromIndex + i);
          }
          return bytes;
      }
docs: Decodes part of a string with <a href="http://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
  
  @param hexDump a {@link CharSequence} which contains the hex dump
  @param fromIndex start of hex dump in {@code hexDump}
  @param length hex string length