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;; Tekuti
;; Copyright (C) 2008, 2010 Andy Wingo <wingo at pobox dot com>
;; Copyright (C) 2009 Andreas Rottmann <a dot rottmann at gmx dot at>
;; This program is free software; you can redistribute it and/or
;; modify it under the terms of the GNU General Public License as
;; published by the Free Software Foundation; either version 3 of
;; the License, or (at your option) any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program; if not, contact:
;;
;; Free Software Foundation Voice: +1-617-542-5942
;; 59 Temple Place - Suite 330 Fax: +1-617-542-2652
;; Boston, MA 02111-1307, USA gnu@gnu.org
;;; Commentary:
;;
;; base 64 y'all
;;
;;; Code:
(define-module (tekuti base64)
#:use-module (rnrs bytevectors)
#:export (base64-encode base64-decode))
(define b64-bytes
(string->utf8
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwzyz0123456789+/"))
(define (int->b64-byte i)
(bytevector-u8-ref b64-bytes (logand i 63)))
(define b64-byte-ranges
(map cons
(map char->integer '(#\A #\a #\0 #\+ #\/))
(map char->integer '(#\Z #\z #\9 #\+ #\/))))
(define (b64-byte->int i)
(let lp ((ranges b64-byte-ranges) (out 0))
(cond ((null? ranges)
(error "bad base64 byte" i))
((and (>= i (caar ranges)) (<= i (cdar ranges)))
(+ out (- i (caar ranges))))
(else
(lp (cdr ranges) (+ out (+ 1 (- (cdar ranges)
(caar ranges)))))))))
(define (bytevector-pad bv n fill)
(let ((result (make-bytevector n fill)))
(bytevector-copy! bv 0 result 0 (bytevector-length bv))
result))
(define-syntax bytevector-map-n-to-m
(lambda (stx)
(syntax-case stx ()
((_ n m)
(with-syntax (((byte-in ...)
(map (lambda (x)
#`(bytevector-u8-ref s (+ i #,x)))
(iota (syntax->datum #'n))))
((byte-out ...)
(generate-temporaries (iota (syntax->datum #'m))))
((byte-out-idx ...)
(iota (syntax->datum #'m))))
#'(lambda (proc s)
(let* ((len (bytevector-length s))
(out (make-bytevector (* len (/ m n)))))
(let lp ((i 0) (j 0))
(cond
((< i len)
(call-with-values (lambda () (proc byte-in ...))
(lambda (byte-out ...)
(bytevector-u8-set! out (+ j byte-out-idx) byte-out)
...))
(lp (+ i n) (+ j m)))
(else out))))))))))
(define (bytevector-fill-range! bv start end u8)
(do ((i (- end 1) (- i 1)))
((< i start))
(bytevector-u8-set! bv i u8)))
(define (bytevector-copy/padding bv npad pad-byte)
(let ((result (bytevector-copy bv))
(len (bytevector-length bv)))
(bytevector-fill-range! result (- len npad) len pad-byte)
result))
(define (base64-encode bv)
(let* ((npad (remainder (- 3 (remainder (bytevector-length bv) 3)) 3))
(out ((bytevector-map-n-to-m 3 4)
(lambda (x y z)
(let ((n (logior (ash x 16) (ash y 8) z)))
(values (int->b64-byte (ash n -18))
(int->b64-byte (ash n -12))
(int->b64-byte (ash n -6))
(int->b64-byte n))))
(bytevector-pad bv (+ (bytevector-length bv) npad) 0))))
(bytevector-fill-range! out
(- (bytevector-length out) npad)
(bytevector-length out)
(char->integer #\=))
(utf8->string out)))
(define eql-byte (char->integer #\=))
(define (b64-bv-npad bv)
(let ((len (bytevector-length bv)))
(if (> len 0)
(if (= (bytevector-u8-ref bv (- len 1)) eql-byte)
(if (> len 1)
(if (= (bytevector-u8-ref bv (- len 2)) eql-byte)
2
1)
1)
0)
0)))
(define (base64-decode str)
(let* ((bv (string->utf8 str))
(npad (b64-bv-npad bv))
(out ((bytevector-map-n-to-m 4 3)
(lambda (w x y z)
(let ((n (logior (ash (b64-byte->int w) 18)
(ash (b64-byte->int x) 12)
(ash (b64-byte->int y) 6)
(b64-byte->int z))))
(values (ash n -16)
(logand (ash n -8) 255)
(logand n 255))))
(bytevector-copy/padding bv npad (char->integer #\A))))
(result (make-bytevector (- (bytevector-length out) npad))))
(bytevector-copy! out 0 result 0 (bytevector-length result))
result))
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