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|
;==============================================================================
; File: "base64.scm", Time-stamp: <2008-12-15 11:54:22 feeley>
; Copyright (c) 2005-2008 by Marc Feeley, All Rights Reserved.
;==============================================================================
(##namespace ("base64#"))
(##include "~~lib/gambit#.scm")
(##include "base64#.scm")
(declare
(standard-bindings)
(extended-bindings)
(block)
(not safe)
(fixnum)
)
;==============================================================================
; Representation of fifos.
(##define-macro (macro-make-fifo)
`(let ((fifo (##cons '() '())))
(macro-fifo-tail-set! fifo fifo)
fifo))
(##define-macro (macro-fifo-next fifo) `(##cdr ,fifo))
(##define-macro (macro-fifo-next-set! fifo x) `(##set-cdr! ,fifo ,x))
(##define-macro (macro-fifo-tail fifo) `(##car ,fifo))
(##define-macro (macro-fifo-tail-set! fifo x) `(##set-car! ,fifo ,x))
(##define-macro (macro-fifo-elem fifo) `(##car ,fifo))
(##define-macro (macro-fifo-elem-set! fifo x) `(##set-car! ,fifo ,x))
(##define-macro (macro-fifo->list fifo)
`(macro-fifo-next ,fifo))
(##define-macro (macro-fifo-remove-all! fifo)
`(let ((fifo ,fifo))
(##declare (not interrupts-enabled))
(let ((head (macro-fifo-next fifo)))
(macro-fifo-tail-set! fifo fifo)
(macro-fifo-next-set! fifo '())
head)))
(##define-macro (macro-fifo-remove-head! fifo)
`(let ((fifo ,fifo))
(##declare (not interrupts-enabled))
(let ((head (macro-fifo-next fifo)))
(if (##pair? head)
(let ((next (macro-fifo-next head)))
(if (##null? next)
(macro-fifo-tail-set! fifo fifo))
(macro-fifo-next-set! fifo next)
(macro-fifo-next-set! head '())))
head)))
(##define-macro (macro-fifo-insert-at-tail! fifo elem)
`(let ((fifo ,fifo) (elem ,elem))
(let ((x (##cons elem '())))
(##declare (not interrupts-enabled))
(let ((tail (macro-fifo-tail fifo)))
(macro-fifo-next-set! tail x)
(macro-fifo-tail-set! fifo x)
(##void)))))
(##define-macro (macro-fifo-insert-at-head! fifo elem)
`(let ((fifo ,fifo) (elem ,elem))
(let ((x (##cons elem '())))
(##declare (not interrupts-enabled))
; To obtain an atomic update of the fifo, we must force a
; garbage-collection to occur right away if needed by the
; ##cons, so that any finalization that might mutate this fifo
; will be done before updating the fifo.
(##check-heap-limit)
(let ((head (macro-fifo-next fifo)))
(if (##null? head)
(macro-fifo-tail-set! fifo x))
(macro-fifo-next-set! fifo x)
(macro-fifo-next-set! x head)
(##void)))))
(##define-macro (macro-fifo-advance-to-tail! fifo)
`(let ((fifo ,fifo))
; It is assumed that the fifo contains at least one element
; (i.e. the fifo's tail does not change).
(let ((new-head (macro-fifo-tail fifo)))
(macro-fifo-next-set! fifo new-head)
(macro-fifo-elem new-head))))
(##define-macro (macro-fifo-advance! fifo)
`(let ((fifo ,fifo))
; It is assumed that the fifo contains at least two elements
; (i.e. the fifo's tail does not change).
(let* ((head (macro-fifo-next fifo))
(new-head (macro-fifo-next head)))
(macro-fifo-next-set! fifo new-head)
(macro-fifo-elem new-head))))
(##define-macro (fifo->u8vector fifo start end)
`(##fifo->u8vector ,fifo ,start ,end))
(##define-macro (u8vector-shrink! u8vect len)
`(##u8vector-shrink! ,u8vect ,len))
(##define-macro (fifo->string fifo start end)
`(##fifo->string ,fifo ,start ,end))
(##define-macro (string-shrink! str len)
`(##string-shrink! ,str ,len))
;==============================================================================
(define base64-string->u8vector
(lambda (str)
(base64-substring->u8vector str 0 (string-length str))))
(define base64-substring->u8vector
(lambda (str start end)
(define err
(lambda ()
(error "base64 decoding error")))
(define chunk-len 64) ; must be a power of 2
(define state
(vector 0
(macro-make-fifo)))
(define (wr-u8 x)
(let ((ptr (vector-ref state 0)))
(vector-set! state 0 (+ ptr 1))
(let ((fifo (vector-ref state 1))
(i (bitwise-and ptr (- chunk-len 1))))
(u8vector-set!
(if (= i 0)
(let ((chunk (make-u8vector chunk-len)))
(macro-fifo-insert-at-tail! fifo chunk)
chunk)
(macro-fifo-elem (macro-fifo-tail fifo)))
i
x))))
(define (get-output-u8vector)
(let ((ptr (vector-ref state 0))
(fifo (vector-ref state 1)))
(if (and (< 0 ptr) (<= ptr chunk-len))
(let ((u8vect (macro-fifo-elem (macro-fifo-tail fifo))))
(u8vector-shrink! u8vect ptr)
u8vect)
(fifo->u8vector fifo 0 ptr))))
(define decode
(lambda (c)
(cond ((and (char>=? c #\A) (char<=? c #\Z))
(- (char->integer c) (char->integer #\A)))
((and (char>=? c #\a) (char<=? c #\z))
(+ 26 (- (char->integer c) (char->integer #\a))))
((and (char>=? c #\0) (char<=? c #\9))
(+ 52 (- (char->integer c) (char->integer #\0))))
((char=? c #\+)
62)
((char=? c #\/)
63)
(else
#f))))
(define done
(lambda ()
(get-output-u8vector)))
(define add1
(lambda (x0 x1)
(add (+ (arithmetic-shift x0 2)
(arithmetic-shift x1 -4)))))
(define add2
(lambda (x0 x1 x2)
(add1 x0 x1)
(add (bitwise-and #xff
(+ (arithmetic-shift x1 4)
(arithmetic-shift x2 -2))))))
(define add3
(lambda (x0 x1 x2 x3)
(add2 x0 x1 x2)
(add (bitwise-and #xff
(+ (arithmetic-shift x2 6)
x3)))))
(define add
(lambda (x)
(wr-u8 x)))
(let loop0 ((i start))
(if (>= i end)
(done)
(let* ((c0 (string-ref str i))
(x0 (decode c0)))
(if x0
(let loop1 ((i (+ i 1)))
(if (>= i end)
(err)
(let* ((c1 (string-ref str i))
(x1 (decode c1)))
(if x1
(let loop2 ((i (+ i 1)))
(if (>= i end)
(err)
(let* ((c2 (string-ref str i))
(x2 (decode c2)))
(if x2
(let loop3 ((i (+ i 1)))
(if (>= i end)
(err)
(let* ((c3 (string-ref str i))
(x3 (decode c3)))
(if x3
(begin
(add3 x0 x1 x2 x3)
(loop0 (+ i 1)))
(if (char=? c3 #\=)
(begin
(add2 x0 x1 x2)
(done))
(loop3 (+ i 1)))))))
(if (char=? c2 #\=)
(begin
(add1 x0 x1)
(done))
(loop2 (+ i 1)))))))
(if (char=? c1 #\=)
(err)
(loop1 (+ i 1)))))))
(if (char=? c0 #\=)
(err)
(loop0 (+ i 1)))))))))
(define u8vector->base64-string
(lambda (u8vect #!optional (width 0))
(subu8vector->base64-string u8vect 0 (u8vector-length u8vect) width)))
(define subu8vector->base64-string
(lambda (u8vect start end #!optional (width 0))
(define chunk-len 64) ; must be a power of 2
(define state
(vector 0
(macro-make-fifo)))
(define (wr-char c)
(let ((ptr (vector-ref state 0)))
(vector-set! state 0 (+ ptr 1))
(let ((fifo (vector-ref state 1))
(i (bitwise-and ptr (- chunk-len 1))))
(string-set!
(if (= i 0)
(let ((chunk (make-string chunk-len)))
(macro-fifo-insert-at-tail! fifo chunk)
chunk)
(macro-fifo-elem (macro-fifo-tail fifo)))
i
c))))
(define (get-output-string)
(let ((ptr (vector-ref state 0))
(fifo (vector-ref state 1)))
(if (and (< 0 ptr) (<= ptr chunk-len))
(let ((str (macro-fifo-elem (macro-fifo-tail fifo))))
(string-shrink! str ptr)
str)
(fifo->string fifo 0 ptr))))
(define add
(lambda (c)
(wr-char c)))
(define out
(lambda (x n)
(let ((new-n
(cond ((= -1 n)
n)
((= 0 n)
(add #\newline)
(- width 1))
(else
(- n 1)))))
(add (cond ((<= x 25)
(integer->char (+ x (char->integer #\A))))
((<= x 51)
(integer->char (+ (- x 26) (char->integer #\a))))
((<= x 61)
(integer->char (+ (- x 52) (char->integer #\0))))
((= x 62)
#\+)
((= x 63)
#\/)
(else
#\=)))
new-n)))
(let loop ((i start)
(n (if (> width 0) width -1)))
(if (<= (+ i 3) end)
(let ((b0 (u8vector-ref u8vect i))
(b1 (u8vector-ref u8vect (+ i 1)))
(b2 (u8vector-ref u8vect (+ i 2))))
(let ((x0
(arithmetic-shift b0 -2))
(x1
(bitwise-and #x3f
(+ (arithmetic-shift b0 4)
(arithmetic-shift b1 -4))))
(x2
(bitwise-and #x3f
(+ (arithmetic-shift b1 2)
(arithmetic-shift b2 -6))))
(x3
(bitwise-and #x3f b2)))
(loop (+ i 3)
(out x3 (out x2 (out x1 (out x0 n)))))))
(let ((rest (- end i)))
(cond ((= rest 2)
(let ((b0 (u8vector-ref u8vect i))
(b1 (u8vector-ref u8vect (+ i 1))))
(let ((x0
(arithmetic-shift b0 -2))
(x1
(bitwise-and #x3f
(+ (arithmetic-shift b0 4)
(arithmetic-shift b1 -4))))
(x2
(bitwise-and #x3f
(arithmetic-shift b1 2)))
(x3
64))
(out x3 (out x2 (out x1 (out x0 n)))))))
((= rest 1)
(let ((b0 (u8vector-ref u8vect i)))
(let ((x0
(arithmetic-shift b0 -2))
(x1
(bitwise-and #x3f
(arithmetic-shift b0 4)))
(x2
64)
(x3
64))
(out x3 (out x2 (out x1 (out x0 n))))))))
(get-output-string))))))
;==============================================================================
|
