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|
; -*- Mode: Scheme; Syntax: Scheme; Package: Scheme; -*-
; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Mike Sperber
(define (encode-scalar-value encoding value buffer count)
(let-syntax ((encode
(syntax-rules ()
((encode ?encode-proc)
(call-with-values
(lambda ()
(?encode-proc value buffer count))
(lambda (encoding-ok? out-of-space? count)
(values #t encoding-ok? out-of-space? count)))))))
(enum-case
text-encoding-option encoding
((us-ascii) (encode encode-scalar-value/us-ascii))
((latin-1) (encode encode-scalar-value/latin-1))
((utf-8) (encode encode-scalar-value/utf-8))
((utf-16le) (encode encode-scalar-value/utf-16le))
((utf-16be) (encode encode-scalar-value/utf-16be))
((utf-32le) (encode encode-scalar-value/utf-32le))
((utf-32be) (encode encode-scalar-value/utf-32be))
(else
(values #f #f #f 0)))))
(define (decode-scalar-value encoding buffer count)
(let-syntax ((decode
(syntax-rules ()
((decode ?decode-proc)
(call-with-values
(lambda () (?decode-proc buffer count))
(lambda (ok? incomplete? value count)
(values #t ok? incomplete? value count)))))))
(enum-case
text-encoding-option encoding
((us-ascii) (decode decode-scalar-value/us-ascii))
((latin-1) (decode decode-scalar-value/latin-1))
((utf-8) (decode decode-scalar-value/utf-8))
((utf-16le) (decode decode-scalar-value/utf-16le))
((utf-16be) (decode decode-scalar-value/utf-16be))
((utf-32le) (decode decode-scalar-value/utf-32le))
((utf-32be) (decode decode-scalar-value/utf-32be))
(else
(values #f #f #f 0 0)))))
;; US-ASCII
;; This is mainly needed because it might be the default locale
;; encoding reported by the OS.
(define (encode-scalar-value/us-ascii value buffer count)
(cond
((< count 1)
(values #t #t 1))
((< value 128)
(buffer-set! buffer 0 value)
(values #t #f 1))
(else
(values #f #f 0))))
(define (decode-scalar-value/us-ascii buffer count)
(values #t ; OK?
#f ; incomplete?
(buffer-ref buffer 0)
1))
; Latin-1
(define (encode-scalar-value/latin-1 value buffer count)
(cond
((< count 1)
(values #t #t 1))
((< value 256)
(buffer-set! buffer 0 value)
(values #t #f 1))
(else
(values #f #f 0))))
(define (decode-scalar-value/latin-1 buffer count)
(values #t ; OK?
#f ; incomplete?
(buffer-ref buffer 0)
1))
; UTF-8
(define (encode-scalar-value/utf-8 value buffer count)
(cond
((<= value #x7f)
(if (>= count 1)
(begin
(buffer-set! buffer 0 value)
(values #t #f 1))
(values #t #t 1)))
((<= value #x7ff)
(if (>= count 2)
(begin
(buffer-set!
buffer 0
(+ #xc0
(logical-shift-right (bitwise-and value #b11111000000)
6)))
(buffer-set!
buffer 1
(+ #x80
(bitwise-and value #b111111)))
(values #t #f 2))
(values #t #t 2)))
((<= value #xffff)
(if (>= count 3)
(begin
(buffer-set!
buffer 0
(+ #xe0
(logical-shift-right (bitwise-and value #b1111000000000000)
12)))
(buffer-set!
buffer 1
(+ #x80
(logical-shift-right (bitwise-and value #b111111000000)
6)))
(buffer-set!
buffer 2
(+ #x80
(bitwise-and value #b111111)))
(values #t #f 3))
(values #t #t 3)))
(else
(if (>= count 4)
(begin
(buffer-set!
buffer 0
(+ #xf0
(logical-shift-right (bitwise-and value #b111000000000000000000)
18)))
(buffer-set!
buffer 1
(+ #x80
(logical-shift-right (bitwise-and value #b111111000000000000)
12)))
(buffer-set!
buffer 2
(+ #x80
(logical-shift-right (bitwise-and value #b111111000000)
6)))
(buffer-set!
buffer 3
(+ #x80
(bitwise-and value #b111111)))
(values #t #f 4))
(values #t #t 4)))))
; The table, and the associated decoding algorithm, is from
; Richard Gillam: "Unicode Demystified", chapter 14
(define *utf-8-state-table*
'#(;; state 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1 2 2 3 -1
;; state 1
-2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 0 0 0 0 0 0 0 0 -2 -2 -2 -2 -2 -2 -2 -2
;; state 2
-2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 1 1 1 1 1 1 1 1 -2 -2 -2 -2 -2 -2 -2 -2
;; state 3
-2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 -2 2 2 2 2 2 2 2 2 -2 -2 -2 -2 -2 -2 -2 -2))
(define *utf-8-masks* '#(#x7f #x1f #x0f #x07))
; We don't check for non-shortest-form UTF-8. Too bad.
(define (decode-scalar-value/utf-8 buffer count)
(let loop ((q 0) (state 0) (mask 0) (scalar-value 0))
(if (< q count)
(let* ((c (buffer-ref buffer q))
(state (vector-ref *utf-8-state-table*
(+ (shift-left state 5) ; (* state 32)
(arithmetic-shift-right c 3)))))
(case state
((0)
(let ((scalar-value (+ scalar-value
(bitwise-and c #x7f))))
(if (scalar-value? scalar-value)
(values #t #f scalar-value (+ q 1))
(values #f #f 0 0))))
((1 2 3)
(loop (+ 1 q) state #x3f
(shift-left (+ scalar-value
(bitwise-and c
(if (= 0 mask)
(vector-ref *utf-8-masks* state)
mask)))
6)))
((-2 -1)
(values #f #f 0 0))
(else ; this can't happen
(values #f #f 0 0))))
(values #t #t 0 (+ 1 q)))))
; UTF-16
(define (buffer-set-word16/le! buffer index word)
(buffer-set! buffer index
(bitwise-and #b11111111 word))
(buffer-set! buffer (+ index 1)
(logical-shift-right word 8)))
(define (buffer-set-word16/be! buffer index word)
(buffer-set! buffer index
(logical-shift-right word 8))
(buffer-set! buffer (+ index 1)
(bitwise-and #b11111111 word)))
(define (make-encode-scalar-value/utf-16 buffer-set-word16!)
(lambda (value buffer count)
(if (<= value #xffff)
(if (< count 2)
(values #t #t 2)
(begin
(buffer-set-word16! buffer 0 value)
(values #t #f 2)))
(if (< count 4)
(values #t #t 4)
(begin
(buffer-set-word16!
buffer 0
(+ (logical-shift-right value 10) #xd7c0))
(buffer-set-word16!
buffer 2
(+ (bitwise-and value #x3ff) #xdc00))
(values #t #f 4))))))
(define encode-scalar-value/utf-16le
(make-encode-scalar-value/utf-16 buffer-set-word16/le!))
(define encode-scalar-value/utf-16be
(make-encode-scalar-value/utf-16 buffer-set-word16/be!))
(define (buffer-ref-word16/le codes index)
(+ (buffer-ref codes index)
(shift-left (buffer-ref codes (+ index 1)) 8)))
(define (buffer-ref-word16/be codes index)
(+ (shift-left (buffer-ref codes index) 8)
(buffer-ref codes (+ index 1))))
(define (make-decode-scalar-value/utf-16 buffer-ref-word16)
(lambda (buffer count)
(if (< count 2)
(values #t #t 0 2)
(let ((word0 (buffer-ref-word16 buffer 0)))
(cond
((or (< word0 #xd800)
(> word0 #xdfff))
(values #t #f word0 2))
((< count 4)
(values #t #t 0 4))
((<= word0 #xdbff)
(let ((word1 (buffer-ref-word16 buffer 2 )))
(if (and (>= word1 #xdc00)
(<= word1 #xdfff))
(values #t #f
(+ (shift-left (- word0 #xd7c0) 10)
(bitwise-and word1 #x3ff))
4)
(values #f #f 0 0))))
(else
(values #f #f 0 0)))))))
(define decode-scalar-value/utf-16le
(make-decode-scalar-value/utf-16 buffer-ref-word16/le))
(define decode-scalar-value/utf-16be
(make-decode-scalar-value/utf-16 buffer-ref-word16/be))
; UTF-32
(define (encode-scalar-value/utf-32le value buffer count)
(if (< count 4)
(values #t #t 4)
(begin
(buffer-set! buffer 0
(bitwise-and value #xff))
(buffer-set! buffer 1
(logical-shift-right
(bitwise-and value #xff00)
8))
(buffer-set! buffer 2
(logical-shift-right
(bitwise-and value #xff0000)
16))
(buffer-set! buffer 3
(logical-shift-right value 24))
(values #t #f 4))))
(define (encode-scalar-value/utf-32be value buffer count)
(if (< count 4)
(values #t #t 4)
(begin
(buffer-set! buffer 0
(logical-shift-right value 24))
(buffer-set! buffer 1
(logical-shift-right
(bitwise-and value #xff0000)
16))
(buffer-set! buffer 2
(logical-shift-right
(bitwise-and value #xff00)
8))
(buffer-set! buffer 3
(bitwise-and value #xff))
(values #t #f 4))))
(define (decode-scalar-value/utf-32le buffer count)
(if (< count 4)
(values #t #t 0 4)
(let ((code-point
(+ (buffer-ref buffer 0)
(shift-left (buffer-ref buffer 1)
8)
(shift-left (buffer-ref buffer 2)
16)
(shift-left (buffer-ref buffer 3)
24))))
(if (scalar-value? code-point)
(values #t #f
code-point
4)
(values #f #f 0 0)))))
(define (decode-scalar-value/utf-32be buffer count)
(if (< count 4)
(values #t #t 0 4)
(let ((code-point
(+ (shift-left (buffer-ref buffer 0)
24)
(shift-left (buffer-ref buffer 1)
16)
(shift-left
(buffer-ref buffer 2)
8)
(buffer-ref buffer 3))))
(if (scalar-value? code-point)
(values #t #f
code-point
4)
(values #f #f 0 0)))))
; Utilities
(define (scalar-value? x)
(and (>= x 0)
(or (<= x #xd7ff)
(and (>= x #xe000) (<= x #x10ffff)))))
(define (buffer-ref b i)
(unsigned-byte-ref (address+ b i)))
(define (buffer-set! b i v)
(unsigned-byte-set! (address+ b i) v))
|
