(setq *Char64
   `'(chop
         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" ) )
(de decode64 (S)
   (let S (chop S)
      (pack
         (make
            (while S
               (let
                  (A (dec (index (++ S) *Char64))
                     B (dec (index (++ S) *Char64))
                     C (dec (index (++ S) *Char64))
                     D (dec (index (++ S) *Char64)) )
                  (link
                     (char (| (>> -2 A) (>> 4 B))) )
                  (and
                     C
                     (link
                        (char
                           (| (>> -4 (& B 15)) (>> 2 C)) ) )
                     D
                     (link
                        (char (| (>> -6 (& C 3)) D)) ) ) ) ) ) ) ) )
(prinl (decode64 "VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLVBhdWwgUi5FaHJsaWNo"))