docs: private static int decode4to3(byte[] src,
                                    int len,
                                    byte[] dest,
                                    int offset) {
          // Example: Dk or Dk==
          if (len == 2 || (src[2] == EQUALS_SIGN && src[3] == EQUALS_SIGN)) {
              int outBuff = (validate(src[0]) << 18) |
                            (validate(src[1]) << 12);
  
              dest[offset] = (byte) (outBuff >>> 16);
              return 1;
          }
  
          // Example: DkL or DkL=
          if (len == 3 || src[3] == EQUALS_SIGN) {
              int outBuff = (validate(src[0]) << 18) |
                            (validate(src[1]) << 12) |
                            (validate(src[2]) << 6);
  
              dest[offset]     = (byte) (outBuff >>> 16);
              dest[offset + 1] = (byte) (outBuff >>> 8);
              return 2;
          }
  
          // Example: DkLE
          int outBuff = (validate(src[0]) << 18) |
                        (validate(src[1]) << 12) |
                        (validate(src[2]) << 6) |
                        (validate(src[3]));
  
          dest[offset]     = (byte) (outBuff >>> 16);
          dest[offset + 1] = (byte) (outBuff >>> 8);
          dest[offset + 2] = (byte) (outBuff);
          return 3;
      }