this.mask = chars.length - 1;

      this.decodabet = decodabet;

      boolean[] validPadding = new boolean[charsPerChunk];
      for (int i = 0; i < bytesPerChunk; i++) {
        validPadding[divide(i * 8, bitsPerChar, CEILING)] = true;
      }
      this.validPadding = validPadding;
      this.ignoreCase = ignoreCase;
    }

    private static byte[] decodabetFor(char[] chars) {