#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme 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 of the License, or (at
your option) any later version.

MIT/GNU Scheme 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 MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; Control Points
;;; package: (runtime control-point)

(declare (usual-integrations))

(define-integrable (control-point? object)
  (object-type? (ucode-type control-point) object))

(define-integrable (control-point/interrupt-mask control-point)
  (control-point-ref control-point 1))

(define-integrable (control-point/history control-point)
  (control-point-ref control-point 3))

(define-integrable (control-point/previous-history-offset control-point)
  (control-point-ref control-point 4))

(define-integrable (control-point/previous-history-control-point control-point)
  (control-point-ref control-point 5))

(define-integrable (control-point-ref control-point index)
  (system-vector-ref control-point (control-point-index index)))

(define-integrable (control-point-index index)
  (fix:+ 2 index))

(define-integrable first-element-index
  (control-point-index 6))

#|

;;; Disabled because some procedures in conpar.scm and environment.scm
;;; depend on the actual length for finding compiled code variables,
;;; etc.

(define (control-point/n-elements control-point)
  (let ((real-length
	 (fix:- (system-vector-length control-point) first-element-index)))
    (if (control-point/next-control-point? control-point)
	(fix:- real-length 2)
	real-length)))
|#

(define (control-point/n-elements control-point)
  (fix:- (system-vector-length control-point) first-element-index))

(define (control-point/element-stream control-point)
  (let ((end
	 (let ((end (system-vector-length control-point)))
	   (if (control-point/next-control-point? control-point)
	       (fix:- end 2)
	       end))))
    (let loop ((index first-element-index))
      (if (fix:< index end)
	  (if ((ucode-primitive primitive-object-type? 2)
	       (ucode-type manifest-nm-vector)
	       (system-vector-ref control-point index))
	      (let ((n-skips
		     (object-datum (system-vector-ref control-point index))))
		(cons-stream
		 (make-non-pointer-object n-skips)
		 (let skip-loop ((n n-skips) (index (fix:+ index 1)))
		   (if (fix:> n 0)
		       (cons-stream #f (skip-loop (fix:- n 1) (fix:+ index 1)))
		       (loop index)))))
	      (cons-stream (map-reference-trap
			    (lambda ()
			      (system-vector-ref control-point index)))
			   (loop (fix:+ index 1))))
	  '()))))

(define (control-point/next-control-point control-point)
  (and (control-point/next-control-point? control-point)
       (system-vector-ref control-point
			  (fix:- (system-vector-length control-point) 1))))

(define (make-control-point interrupt-mask
			    history
			    previous-history-offset
			    previous-history-control-point
			    element-stream
			    next-control-point)
  (let ((result
	 (make-vector (+ first-element-index
			 (stream-length element-stream)
			 (if next-control-point 2 0))))
	(index 0))
    (let ((assign
	   (lambda (value)
	     (vector-set! result index value)
	     (set! index (fix:+ index 1))
	     unspecific)))
      ;; The first two elements are unused artifacts from the old days
      ;; when "stacklets" were used.
      (assign #f)
      (assign (make-non-pointer-object 0))
      (assign (ucode-return-address restore-interrupt-mask))
      (assign interrupt-mask)
      (assign (ucode-return-address restore-history))
      (assign history)
      (assign previous-history-offset)
      (assign previous-history-control-point)
      (stream-for-each (lambda (element)
			 (assign (unmap-reference-trap element)))
		       element-stream)
      (if next-control-point
	  (begin
	    (assign (ucode-return-address join-stacklets))
	    (assign next-control-point))))
    (object-new-type (ucode-type control-point) result)))

(define (control-point/next-control-point? control-point)
  ((ucode-primitive primitive-object-eq? 2)
   (system-vector-ref control-point
		      (fix:- (system-vector-length control-point) 2))
   (ucode-return-address join-stacklets)))