module/language/objcode.scm

   1 ;;; Guile Virtual Machine Object Code
   2
   3 ;; Copyright (C) 2001 Free Software Foundation, Inc.
   4
   5 ;; This program is free software; you can redistribute it and/or modify
   6 ;; it under the terms of the GNU General Public License as published by
   7 ;; the Free Software Foundation; either version 2, or (at your option)
   8 ;; any later version.
   9 ;;
  10 ;; This program is distributed in the hope that it will be useful,
  11 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 ;; GNU General Public License for more details.
  14 ;;
  15 ;; You should have received a copy of the GNU General Public License
  16 ;; along with this program; see the file COPYING.  If not, write to
  17 ;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18 ;; Boston, MA 02111-1307, USA.
  19
  20 ;;; Code:
  21
  22 (define-module (language objcode)
  23   #:export (encode-length decode-length))
  24
  25 \f
  26 ;;;
  27 ;;; Variable-length interface
  28 ;;;
  29
  30 ;; NOTE: decoded in vm_fetch_length in vm.c as well.
  31
  32 (define (encode-length len)
  33   (cond ((< len 254) (u8vector len))
  34         ((< len (* 256 256))
  35          (u8vector 254 (quotient len 256) (modulo len 256)))
  36         ((< len most-positive-fixnum)
  37          (u8vector 255
  38                    (quotient len (* 256 256 256))
  39                    (modulo (quotient len (* 256 256)) 256)
  40                    (modulo (quotient len 256) 256)
  41                    (modulo len 256)))
  42         (else (error "Too long code length:" len))))
  43
  44 (define (decode-length pop)
  45   (let ((x (pop)))
  46     (cond ((< x 254) x)
  47           ((= x 254) (+ (ash x 8) (pop)))
  48           (else
  49            (let* ((b2 (pop))
  50                   (b3 (pop))
  51                   (b4 (pop)))
  52              (+ (ash x 24) (ash b2 16) (ash b3 8) b4))))))