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(defpackage dawg.octet-stream
(:use :common-lisp :dawg.global)
(:shadow :common-lisp read peek position)
(:export make
read
peek
eos?
eat
position))
(in-package :dawg.octet-stream)
;;;;;;;;;;;;;;;;
;;; declamation
(declaim #.*fastest*
(inline make-octet-stream make eos? octet-length peek read eat position))
;;;;;;;;;;;;;;;;
;;; octet-stream
(defstruct octet-stream
(src "" :type simple-characters)
(pos 0 :type array-index)
(end 0 :type array-index)
(code 0 :type unicode)
(octet-pos 0 :type (mod 5))
(octet-len 0 :type (mod 5)))
;;;;;;;;;;;;;;;;;;;;;;
;;; auxiliary function
(defun octet-length (code)
(declare (unicode code))
(cond ((< code #x80) 1)
((< code #x800) 2)
((< code #x10000) 3)
(t 4)))
;;;;;;;;;;;;;;;;;;;;;
;;; external function
(defun position (in)
(octet-stream-pos in))
(defun make (string &key (start 0) (end (length string)))
(declare (simple-characters string)
(array-index start end))
(let* ((code (if (= start (length string))
0
(char-code (char string start))))
(len (octet-length code)))
(make-octet-stream :src string :pos start :end end
:code code :octet-pos len :octet-len len)))
(defun eos? (in)
(with-slots ( pos end) (the octet-stream in)
(= pos end)))
(defun peek (in)
(with-slots (code octet-pos octet-len) (the octet-stream in)
(if (= octet-pos octet-len)
(case octet-len
(1 code)
(2 (+ #b11000000 (ldb (byte 5 6) code)))
(3 (+ #b11100000 (ldb (byte 4 12) code)))
(t (+ #b11110000 (ldb (byte 3 18) code))))
(+ #b10000000 (ldb (byte 6 (* (the (mod 4) (1- octet-pos)) 6)) code)))))
(defun eat (in)
(with-slots (src pos code octet-pos octet-len) (the octet-stream in)
(decf octet-pos)
(when (zerop octet-pos)
(incf pos)
(unless (eos? in)
(setf code (char-code (char src pos))
octet-len (octet-length code)
octet-pos octet-len))))
in)
(defun read (in)
(prog1 (peek in)
(eat in)))
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