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;;; Guile Virtual Machine Object Code
;; Copyright (C) 2001 Free Software Foundation, Inc.
;; 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 2, 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; see the file COPYING. If not, write to
;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Code:
(define-module (language objcode)
#:export (encode-length decode-length))
;;;
;;; Variable-length interface
;;;
;; NOTE: decoded in vm_fetch_length in vm.c as well.
(define (encode-length len)
(cond ((< len 254) (u8vector len))
((< len (* 256 256))
(u8vector 254 (quotient len 256) (modulo len 256)))
((< len most-positive-fixnum)
(u8vector 255
(quotient len (* 256 256 256))
(modulo (quotient len (* 256 256)) 256)
(modulo (quotient len 256) 256)
(modulo len 256)))
(else (error "Too long code length:" len))))
(define (decode-length pop)
(let ((x (pop)))
(cond ((< x 254) x)
((= x 254) (+ (ash x 8) (pop)))
(else
(let* ((b2 (pop))
(b3 (pop))
(b4 (pop)))
(+ (ash x 24) (ash b2 16) (ash b3 8) b4))))))
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