#| -*-Scheme-*-

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    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, 2020 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)))