source: trunk/j/src/org/armedbear/lisp/mask-field.lisp @ 4562

Last change on this file since 4562 was 4562, checked in by piso, 19 years ago

Initial checkin.

File size: 1.4 KB
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1;;; mask-field.lisp
2;;;
3;;; Copyright (C) 2003 Peter Graves
4;;; $Id: mask-field.lisp,v 1.1 2003-10-28 23:25:51 piso Exp $
5;;;
6;;; This program is free software; you can redistribute it and/or
7;;; modify it under the terms of the GNU General Public License
8;;; as published by the Free Software Foundation; either version 2
9;;; of the License, or (at your option) any later version.
10;;;
11;;; This program is distributed in the hope that it will be useful,
12;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14;;; GNU General Public License for more details.
15;;;
16;;; You should have received a copy of the GNU General Public License
17;;; along with this program; if not, write to the Free Software
18;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
19
20;;; From CMUCL.
21
22(defun mask-field (bytespec integer)
23  (let ((size (byte-size bytespec))
24        (pos (byte-position bytespec)))
25    (logand integer (ash (1- (ash 1 size)) pos))))
26
27(define-setf-expander mask-field (bytespec place &environment env)
28  (multiple-value-bind (dummies vals newval setter getter)
29    (get-setf-expansion place env)
30    (let ((btemp (gensym))
31    (gnuval (gensym)))
32      (values (cons btemp dummies)
33        (cons bytespec vals)
34        (list gnuval)
35        `(let ((,(car newval) (deposit-field ,gnuval ,btemp ,getter)))
36     ,setter
37     ,gnuval)
38        `(mask-field ,btemp ,getter)))))
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