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;; Copyright (c) 2011 Phil Hargett
;; Permission is hereby granted, free of charge, to any person obtaining a copy
;; of this software and associated documentation files (the "Software"), to deal
;; in the Software without restriction, including without limitation the rights
;; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
;; copies of the Software, and to permit persons to whom the Software is
;; furnished to do so, subject to the following conditions:
;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.
;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
;; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
;; THE SOFTWARE.
;;
;; Base32 encoding - http://tools.ietf.org/html/rfc4648
;;
;; Adapted for eris-cl
(in-package :eris)
(define-constant +base32-alphabet+ "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567" :test #'equalp)
(defun encode-word (a-word)
"Return the digit in the base32 alphabet corresponding to a word"
(char +base32-alphabet+ a-word))
(defun decode-word (a-digit)
"Return the word encoded as a digit in the base32 alphabet"
(let ((code (char-code a-digit)))
(or (and (char<= #\a a-digit #\z)
(- code (char-code #\a)))
(and (char<= #\2 a-digit #\7)
(+ 26 (- code (char-code #\2))))
;; upper case
(and (char<= #\A a-digit #\Z)
(- code (char-code #\A))))))
(defun read-word (some-bytes word-index)
"Return the word (a 5-bit integer) found in some-bytes located at word-index"
(let* ((bytes-length (length some-bytes))
;; don't be confused : bit indexes aren't really pointing to
;; the bit as understood by Lisp--they are more virtual in nature,
;; which assumes that bit 0 is the MSB rather than bit 8 being MSB
(start-bit-index (* 5 word-index) )
(end-bit-index (+ 4 start-bit-index) )
(part1-byte-index (floor start-bit-index 8))
(part2-byte-index (floor end-bit-index 8))
(part1-size (min 5 (- 8 (mod start-bit-index 8))))
(part2-size (- 5 part1-size))
;; here we translate the bit indexes so that the MSB is bit 8
;; and the LSB is bit 0
(source-part1 (byte part1-size
(- (- 8 (mod start-bit-index 8)) part1-size)
)
)
(source-part2 (byte part2-size
(- (- 8 (mod end-bit-index 8)) 1) )
)
;; becomes the upper bits in value
(dest-part1 (byte part1-size part2-size))
;; becomes the lower bits in value
(dest-part2 (byte part2-size 0))
(value 0))
(setf (ldb dest-part1 value)
(ldb source-part1 (aref some-bytes part1-byte-index)))
(if (< part1-byte-index bytes-length)
(if (> part2-byte-index part1-byte-index)
(if (< part2-byte-index (length some-bytes))
(setf (ldb dest-part2 value)
(ldb source-part2 (aref some-bytes part2-byte-index)))
(setf (ldb dest-part2 value) 0 )))
(setq value 0))
value))
(defun write-word (some-bytes word-index word)
"Write the word into the bits located at word-index in some-bytes"
(let* (
(bytes-length (length some-bytes))
;; don't be confused : bit indexes aren't really pointing to
;; the bit as understood by Lisp--they are more virtual in nature,
;; which assumes that bit 0 is the MSB rather than bit 8 being MSB
(start-bit-index (* 5 word-index) )
(end-bit-index (+ 4 start-bit-index) )
(part1-byte-index (floor start-bit-index 8))
(part2-byte-index (floor end-bit-index 8))
(part1-size (min 5 (- 8 (mod start-bit-index 8))))
(part2-size (- 5 part1-size))
;; here we translate the bit indexes so that the MSB is bit 8
;; and the LSB is bit 0
(dest-part1 (byte part1-size
(- (- 8 (mod start-bit-index 8)) part1-size)))
(dest-part2 (byte part2-size
(- (- 8 (mod end-bit-index 8)) 1) ))
;; becomes the upper bits in value
(source-part1 (byte part1-size part2-size))
;; becomes the lower bits in value
(source-part2 (byte part2-size 0))
(part1-byte (aref some-bytes part1-byte-index))
(part2-byte (if (and (< part2-byte-index bytes-length)
(> part2-size 0))
(aref some-bytes part2-byte-index))))
(setf (ldb dest-part1 part1-byte)
(ldb source-part1 word))
(if part2-byte
(setf (ldb dest-part2 part2-byte)
(ldb source-part2 word)))
(setf (aref some-bytes part1-byte-index) part1-byte)
(if part2-byte
(setf (aref some-bytes part2-byte-index) part2-byte))))
(defun unpadded-base32-length (base32-string)
"Given a base32 string, compute the size of the raw base32 string,
without any = padding
"
(let* ((padded-length (length base32-string))
(unpadded-length padded-length))
(dotimes (i padded-length)
(if (eql #\= (aref base32-string (- padded-length i)))
(decf unpadded-length)
(return unpadded-length)))))
(defun byte-length-from-base32 (base32-string)
"Given a base32 string, compute the number of bytes in the
decoded data
"
(let* ((padded-length (length base32-string))
(unpadded-length padded-length)
(padding 0)
(block-count (ceiling padded-length 8)))
(if (<= padded-length 0)
0
(progn
(dotimes (i padded-length)
(if (eql #\= (aref base32-string (- padded-length i 1)))
(progn
(decf unpadded-length)
(incf padding))))
(- (* 5 block-count)
(ecase padding
(0 0)
(6 4)
(4 3)
(3 2)
(1 1)))))))
(defun base32-length-from-bytes (some-bytes)
"Given bytes of unencoded data, determine the length of the
corresponding base32-encoded string
"
(let* ((word-count (ceiling (* 8 (length some-bytes)) 5) )
(digit-count (* 8 (ceiling word-count 8))))
(values digit-count word-count)))
(defun bytes-to-base32 (some-bytes)
"Return a base32 string encoding of the provided vector of bytes"
(let* ((word-count (ceiling (* 8 (length some-bytes)) 5) )
(digit-count (* 8 (ceiling word-count 8)))
(base32-string (make-string digit-count :initial-element #\=)))
(dotimes (i word-count)
(setf (aref base32-string i)
(encode-word (read-word some-bytes i))))
base32-string))
(defun base32-to-bytes (base32-string)
"Return the bytes decoded from the supplied base32 string"
(let* ((byte-count (byte-length-from-base32 base32-string) )
(base32-bytes (make-array `(,byte-count)
:element-type '(unsigned-byte 8)
:initial-element 0)))
(dotimes (i (length base32-string))
(let ((word (decode-word (aref base32-string i))))
(if word
(write-word base32-bytes i word)
(return nil))))
base32-bytes))
(defun base32-to-bytes-unpadded (base32-string)
(let ((padding (make-array (- 8 (mod (length base32-string) 8)) :element-type 'character :initial-element #\=)))
(base32-to-bytes (concatenate 'string base32-string padding))))
(defun bytes-to-base32-unpadded (bytes)
(let ((string (bytes-to-base32 bytes)))
(subseq string 0 (position #\= string))))
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