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|
(in-package "ACL2")
;; definition of a tiny machine + its safe version + its bcv.
;;
;; with ifeq, push, pop, invoke, return, halt
;------------------------------------------------------------
;
; The SMALL Machine (with a more "correct" BCV)
;
;------------------------------------------------------------
(include-book "misc/records" :dir :system)
; Stacks
(defun pushx (obj stack) (cons obj stack))
(defun topx (stack) (car stack))
(defun popx (stack) (cdr stack))
; Alists
(defun bound? (x alist) (assoc-equal x alist))
(defun bind (x y alist)
(cond ((endp alist) (list (cons x y)))
((equal x (car (car alist)))
(cons (cons x y) (cdr alist)))
(t (cons (car alist) (bind x y (cdr alist))))))
(defun binding (x alist) (cdr (bound? x alist)))
; Instructions
(defun op-code (inst) (car inst))
(defun arg (inst) (car (cdr inst)))
(defun popStack (st)
(let* ((call-stack (g 'call-stack st))
(top-frame (topx call-stack))
(op-stack (g 'op-stack top-frame)))
(s 'call-stack
(pushx (s 'op-stack
(popx op-stack)
top-frame)
(popx call-stack))
st)))
(defun pushStack (v st)
(let* ((call-stack (g 'call-stack st))
(top-frame (topx call-stack))
(op-stack (g 'op-stack top-frame)))
(s 'call-stack
(pushx (s 'op-stack
(pushx v op-stack)
top-frame)
(popx call-stack))
st)))
(defun topStack (st)
(let* ((call-stack (g 'call-stack st))
(top-frame (topx call-stack))
(op-stack (g 'op-stack top-frame)))
(topx op-stack)))
(defun set-pc (pc st)
(let* ((call-stack (g 'call-stack st))
(top-frame (topx call-stack)))
(s 'call-stack
(pushx (s 'pc pc top-frame)
(popx call-stack))
st)))
(defun get-pc (st)
(g 'pc (topx (g 'call-stack st))))
;----------------------------------------------------------------------
;----------------------------------------------------------------------
(defun execute-IFEQ (inst st)
(let* ((target (arg inst))
(v (topstack st))
(pc (get-pc st)))
(if (equal v 0)
(set-pc target
(popStack st))
(set-pc (+ 1 pc)
(popStack st)))))
;----------------------------------------------------------------------
(defun execute-PUSH (inst st)
(let* ((v (arg inst))
(pc (get-pc st)))
(set-pc (+ 1 pc)
(pushStack v st))))
;----------------------------------------------------------------------
(defun createInitFrame (method-name initial-locals st)
(s 'max-stack (g 'max-stack
(binding method-name (g 'method-table st)))
(s 'pc 0
(s 'method-name method-name
(s 'locals initial-locals
(s 'op-stack nil nil))))))
(defun pushInitFrame (method-name initial-locals st)
(s 'call-stack
(pushx
(createInitFrame method-name initial-locals st)
(g 'call-stack st))
st))
(defun op-stack (st)
(g 'op-stack
(topx (g 'call-stack st))))
(defun popStack-n (st n)
(if (zp n) st
(popStack-n (popStack st)
(- n 1))))
(defun init-locals (stack n)
(if (zp n) nil
(s n (topx stack)
(init-locals (popx stack) (- n 1)))))
(defun execute-INVOKE (inst st)
(let* ((method-name (arg inst))
(method-table (g 'method-table st))
(method (binding method-name method-table))
(nargs (g 'nargs method)))
(pushInitFrame
method-name
(init-locals (op-stack st) nargs)
(set-pc (+ 1 (get-pc st))
;;
;; we could avoid modifying the pc
;; and make the return instruction to modify the pc of caller
;; however we still face the problem that
;; the caller's operand stack does not comply with the signature
;;
(popStack-n st nargs)))))
;----------------------------------------------------------------------
(defun execute-HALT (inst st)
(declare (ignore inst))
st)
;----------------------------------------------------------------------
(defun execute-POP (inst st)
(declare (ignore inst))
(set-pc (+ 1 (get-pc st))
(popStack st)))
;----------------------------------------------------------------------
(defun execute-RETURN (inst st)
(declare (ignore inst))
;; update it to halt, when we know this is the very first frame!! or update
;; our consistent-state predicate!
(if (not (consp (popx (g 'call-stack st))))
st
(pushStack
(topStack st)
(s 'call-stack
(popx (g 'call-stack st))
st))))
;----------------------------------------------------------------------
(defun current-method (st)
(let* ((method-name (g 'method-name (topx (g 'call-stack st))))
(method-table (g 'method-table st)))
(binding method-name method-table)))
(defun pc-in-range (st)
(let ((pc (g 'pc (topx (g 'call-stack st))))
(code (g 'code (binding (g 'method-name
(topx (g 'call-stack st)))
(g 'method-table st)))))
(and (integerp pc)
(<= 0 pc)
(< pc (len code)))))
(defun next-inst (st)
(let* ((pc (get-pc st))
(code (g 'code (current-method st))))
(if (not (pc-in-range st))
nil
(nth pc code))))
;----------------------------------------------------------------------
(defun m-step (st)
(let* ((inst (next-inst st))
(opcode (op-code inst)))
(cond ((equal opcode 'INVOKE)
(execute-INVOKE inst st))
((equal opcode 'PUSH)
(execute-PUSH inst st))
((equal opcode 'IFEQ)
(execute-IFEQ inst st))
((equal opcode 'HALT)
(execute-HALT inst st))
((equal opcode 'POP)
(execute-POP inst st))
((equal opcode 'RETURN)
(execute-RETURN inst st))
(t st))))
;----------------------------------------------------------------------
(defun m-run (st n)
(if (zp n) st
(m-run (m-step st) (- n 1))))
;----------------------------------------------------------------------
|
