(in-package :araneida) ;;;; This assumes an ASCII-based character set.  It's not the fastest ;;;; base64 decoder in the world either, I expect - but presently it's ;;;; only used for http basic authentication header decoding (defun base64-decode-quad (q)   (declare (optimize (speed 3)))   (labels ((lookup (c)                    (or                     (position c                               "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/") 0)))     (destructuring-bind (q1 q2 q3 q4 &rest ignored) q       (declare (ignore ignored))       (let ((val (coerce 0 '(unsigned-byte 32))))         (setf (ldb (byte 6 0) val) (lookup q4))         (setf (ldb (byte 6 6) val) (lookup q3))         (setf (ldb (byte 6 12) val) (lookup q2))         (setf (ldb (byte 6 18) val) (lookup q1))         (let ((v1 (ldb (byte 8 16) val))               (v2 (ldb (byte 8 8) val))               (v3 (ldb (byte 8 0) val)))           (list (code-char v1) (code-char v2) (code-char v3))))))) (defun base64-decode (string)   "Decode the MIME Base64-encoded data in STRING, as per RFC1521 section 5.2"   ;; (1) Delete all the characters not in the set [A-Za-z0-9+=]  ;; (2) assert string length is a multiple of 4  ;; (3) strip all #\= from end of string  ;; (4) assign each byte a number 0-63 based on its position in the  ;;    set A-Za-z0-9+/  ;; (5) iterate over the string in 4-character chunks.  For each  ;;    chunk, output 3 characters  (let ((len (truncate (* (or (position #\= string) (length string)) .75))))     (subseq      (coerce       (loop for q on (coerce string 'list) by #'cddddr             for out-chunk = (base64-decode-quad q)             append out-chunk)       'string)      0 len)))