<* PRAGMA SPEC *>

UNSAFE MODULE JunoRT EXPORTS JunoRT, JunoArgs;

IMPORT JunoRTError, JunoMarshal, JunoSolve, JunoValue, RTVal;
IMPORT   QId, QIdIntTbl, JunoByteCode AS BC;
IMPORT Atom, RefIntTbl, Word, Thread;

IMPORT Wr, Fmt, JunoDisassem;
FROM Stdio IMPORT stderr;
<* FATAL Wr.Failure, Thread.Alerted *>

TYPE
  JVIntTbl = RefIntTbl.Default BRANDED "JunoRT.JVIntTbl" OBJECT OVERRIDES
    keyEqual := JVEqual;
    keyHash := JVHash
  END;

PROCEDURE JVEqual(<*UNUSED*> t: JVIntTbl; READONLY k1, k2: REFANY): BOOLEAN =
  BEGIN RETURN JunoValue.Equal(k1, k2) END JVEqual;

PROCEDURE JVHash(<*UNUSED*> t: JVIntTbl; READONLY k: REFANY): Word.T =
  BEGIN RETURN JunoValue.Hash(k) END JVHash;

VAR
  val_idx_tbl := NEW(JVIntTbl).init(sizeHint := 20);
  var_idx_tbl, code_idx_tbl, ext_idx_tbl :=
    NEW(QIdIntTbl.Default).init(sizeHint:=20);
  next_var_idx := 1;
  next_code_idx := 1;
  next_ext_idx := 0;
  procAttrs: REF ARRAY OF ProcAttr;
  extProcAttrs: REF ARRAY OF ProcAttr;

PROCEDURE GetValueIndex(val: JunoValue.T): CARDINAL =
  VAR res: INTEGER; BEGIN
    IF NOT val_idx_tbl.get(val, res) THEN
      res := next_var_idx;
      INC(next_var_idx);
      EVAL val_idx_tbl.put(val, res);
      VAR n := NUMBER(value_tbl^); BEGIN
        IF next_var_idx = n THEN
          VAR new := NEW(REF ARRAY OF JunoValue.T, 2 * n); BEGIN
            SUBARRAY(new^, 0, n) := value_tbl^;
            value_tbl := new
          END
        END
      END;
      value_tbl[res] := val
    END;
    RETURN res
  END GetValueIndex;

PROCEDURE GetVarIndex(md, nm: Atom.T): CARDINAL =
  VAR res: INTEGER; qid := NEW(QId.T, id0 := md, id1 := nm); BEGIN
    IF NOT var_idx_tbl.get(qid, res) THEN
      res := next_var_idx;
      INC(next_var_idx);
      EVAL var_idx_tbl.put(qid, res);
      VAR n := NUMBER(value_tbl^); BEGIN
        IF next_var_idx = n THEN
          VAR new := NEW(REF ARRAY OF JunoValue.T, 2 * n); BEGIN
            SUBARRAY(new^, 0, n) := value_tbl^;
            value_tbl := new
          END
        END
      END
    END;
    RETURN res
  END GetVarIndex;

PROCEDURE GetCodeIndex(READONLY pa: ProcAttr): CARDINAL =
  VAR res: INTEGER; qid := NEW(QId.T, id0 := pa.modName, id1 := pa.name); BEGIN
    IF NOT code_idx_tbl.get(qid, res) THEN
      res := next_code_idx; INC(next_code_idx);
      EVAL code_idx_tbl.put(qid, res);
      VAR n := NUMBER(code_tbl^); BEGIN
        IF next_code_idx = n THEN
          VAR new := NEW(REF ARRAY OF ByteStream, 2 * n); BEGIN
            SUBARRAY(new^, 0, n) := code_tbl^;
            code_tbl := new
          END;
          VAR new := NEW(REF ARRAY OF ProcAttr, 2 * n); BEGIN
            SUBARRAY(new^, 0, n) := procAttrs^;
            procAttrs := new
          END
        END
      END
    END;
    procAttrs[res] := pa;
    RETURN res
  END GetCodeIndex;

PROCEDURE GetExtCodeIndex(READONLY pa: ProcAttr): CARDINAL =
  VAR res: INTEGER; qid := NEW(QId.T, id0 := pa.modName, id1 := pa.name); BEGIN
    IF NOT ext_idx_tbl.get(qid, res) THEN
      res := next_ext_idx; INC(next_ext_idx);
      EVAL ext_idx_tbl.put(qid, res);
      VAR n := NUMBER(ext_code_tbl^); BEGIN
        IF next_ext_idx = n THEN
          VAR new := NEW(REF ARRAY OF ExternalCode, 2 * n); BEGIN
            SUBARRAY(new^, 0, n) := ext_code_tbl^;
            ext_code_tbl := new
          END;
          VAR new := NEW(REF ARRAY OF ProcAttr, 2 * n); BEGIN
            SUBARRAY(new^, 0, n) := extProcAttrs^;
            extProcAttrs := new
          END
        END
      END
    END;
    extProcAttrs[res] := pa;
    RETURN res
  END GetExtCodeIndex;

PROCEDURE GetProcAttr(s: CARDINAL): ProcAttr =
  BEGIN RETURN procAttrs[s] END GetProcAttr;

PROCEDURE GetExtProcAttr(s: CARDINAL): ProcAttr =
  BEGIN RETURN extProcAttrs[s] END GetExtProcAttr;

TYPE
  CallState = RTVal.T OBJECT
    pc: PC;
    fp: CARDINAL;
    clIns: CARDINAL;
    nextAvail: CallState;
  END;

TYPE
  BytePtr = JunoMarshal.BytePtr;
  Real = JunoValue.Real;
  StackValue = RTVal.T;

CONST
  InitialProc = 0;
  BaseFP = LAST(CARDINAL);
  NoTrapLoc = PC{InitialProc, 0};
  NoErrorCode = JunoRTError.Code.None;

The value NoErrorCode is assigned to the errorCode field of an ExecRes record in the event of a non-error trap-code.

VAR
  (* state variables *)
  stackSize: CARDINAL := 10000;
  stack := NEW(REF ARRAY OF StackValue, stackSize);
  pc := PC{InitialProc, 0};		 (* program counter *)
  fp: CARDINAL := BaseFP;		 (* frame pointer (into stack) *)
  sp: CARDINAL := 0;			 (* stack pointer (into stack) *)
  ext_fp: CARDINAL;			 (* frame pointer for external proc *)
  cond: BOOLEAN;			 (* condition flag *)

VAR
  (* saved state *)
  saved_pc: PC;
  saved_fp, saved_sp: CARDINAL;
  saved_stack: REF ARRAY OF StackValue;
  saved_cond: BOOLEAN;

REVEAL
  Frame = FramePublic BRANDED "JunoRT.Frame" OBJECT
    fp: CARDINAL;
    downF, upF: Frame;
  OVERRIDES
    down     := FrameDown;
    up       := FrameUp;
    getLocal := GetLocal;
    setLocal := SetLocal;
    pc       := GetPC;
    setPC    := SetPC
  END;

VAR
  topFrame: Frame;
  baseFrame: Frame;

PROCEDURE FrameDown(f: Frame): Frame =
  BEGIN
    RETURN f.downF
  END FrameDown;

PROCEDURE FrameUp(f: Frame): Frame =
  BEGIN
    RETURN f.upF
  END FrameUp;

PROCEDURE GetLocal(f: Frame; i: INTEGER): JunoValue.T =
  BEGIN
    <* ASSERT i # 0 *>
    RETURN RTVal.ToJV(stack[f.fp + i])
  END GetLocal;

PROCEDURE SetLocal(f: Frame; i: INTEGER; v: JunoValue.T) =
  BEGIN
    <* ASSERT i # 0 *>
    stack[f.fp + i] := RTVal.FromJV(v)
  END SetLocal;

PROCEDURE GetPC(f: Frame): PC =
  BEGIN
    IF f = topFrame
      THEN RETURN pc
      ELSE RETURN NARROW(stack[f.upF.fp], CallState).pc
    END
  END GetPC;

PROCEDURE SetPC(f: Frame; newPC: PC) =
  BEGIN
    IF f = topFrame
      THEN pc := newPC
      ELSE NARROW(stack[f.upF.fp], CallState).pc := newPC
    END
  END SetPC;

PROCEDURE BaseFrame(): Frame =
  BEGIN
    RETURN baseFrame
  END BaseFrame;

PROCEDURE TopFrame(): Frame =
  BEGIN
    RETURN topFrame
  END TopFrame;

PROCEDURE PushFrame(new_pc: PC; size: CARDINAL) =
  VAR st := MakeCallState(pc, fp); BEGIN
    WHILE sp + size + 1 > stackSize DO EnlargeStack() END;
    <* FATAL StackOverflow, PushedNIL *>
    BEGIN
      FOR i := 1 TO size DO Push(RTVal.nil) END;
      Push(st)
    END;
    fp := sp - 1;
    topFrame.upF := NEW(Frame, downF := topFrame, upF := NIL, fp := fp);
    topFrame := topFrame.upF;
    pc := new_pc
  END PushFrame;

PROCEDURE PopFrame() =

PopFrame pops the frame, but leaves any arguments on the stack, so that it appears to the code in the frame above that the procedure has genuinely returned.

  VAR st: CallState := stack[fp]; BEGIN
    sp := fp;
    fp := st.fp;
    pc := st.pc;
    DisposeCallState(st);
    topFrame := topFrame.downF
  END PopFrame;

PROCEDURE RecomputeFrames() =

Create a new chain of stack frames corresponding to the current frames on the run-time stack beginning at fp. Set topFrame and baseFrame to the bottom and top stack frames, respectively.

  VAR curr_fp := fp; BEGIN
    topFrame := NEW(Frame, downF := NIL, upF := NIL, fp := curr_fp);
    VAR f := topFrame; BEGIN
      WHILE curr_fp # BaseFP DO
        curr_fp := NARROW(stack[f.fp], CallState).fp;
        f.downF := NEW(Frame, upF := f, downF := NIL, fp := curr_fp);
        f := f.downF
      END;
      baseFrame := f
    END
  END RecomputeFrames;

EXCEPTION StackOverflow; PushedNIL;

PROCEDURE Push(v: StackValue) RAISES { StackOverflow, PushedNIL } =
  BEGIN
    IF v = NIL THEN RAISE PushedNIL END;
    IF sp = stackSize THEN RAISE StackOverflow END;
    stack[sp] := v;
    INC(sp)
  END Push;

PROCEDURE Pop(): StackValue =
  BEGIN
    DEC(sp);
    RETURN stack[sp]
  END Pop;

PROCEDURE PopNum(VAR (*INOUT*) err: BOOLEAN): RTVal.Real =
  BEGIN
    DEC(sp);
    TYPECASE stack[sp] OF
      NULL => (* SKIP *)
    | RTVal.Number (r) => RETURN r.val
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN 0.0
  END PopNum;

PROCEDURE PopText(VAR (*INOUT*) err: BOOLEAN): TEXT =
  BEGIN
    DEC(sp);
    TYPECASE stack[sp] OF
      NULL => (* SKIP *)
    | RTVal.Text (r)  => RETURN r.val
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN NIL
  END PopText;

PROCEDURE PopPair(VAR (*INOUT*) err: BOOLEAN): RTVal.Pair =
  BEGIN
    DEC(sp);
    TYPECASE stack[sp] OF
      NULL => (* SKIP *)
    | RTVal.Pair (r)  => RETURN r
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN NIL
  END PopPair;

PROCEDURE InsertList(l: RTVal.T; lSz, numBelow: CARDINAL)
  RAISES {StackOverflow} =

Insert the lSz values of l onto the stack in order under the top numBelow elements.

  VAR oldSp := sp; BEGIN
    IF sp + lSz >= stackSize THEN RAISE StackOverflow END;
    INC(sp, lSz);
    SUBARRAY(stack^, sp - numBelow, numBelow) :=
      SUBARRAY(stack^, oldSp - numBelow, numBelow);
    VAR i := oldSp - numBelow; BEGIN
      WHILE l # RTVal.nil DO
      	VAR pr: RTVal.Pair := l; BEGIN
      	  stack[i] := pr.car;
      	  l := pr.cdr
      	END;
        INC(i)
      END
    END
  END InsertList;

PROCEDURE PopList(n: CARDINAL): RTVal.T =

Pop and return the list of the top n elements of the stack, where the top of the stack becomes the last element of the list.

  VAR
    res: RTVal.T := RTVal.nil;
  BEGIN
    FOR i := 1 TO n DO
      res := RTVal.FromPair(Pop(), res)
    END;
    RETURN res
  END PopList;

PROCEDURE ReadValue(i: CARDINAL): RTVal.T =
  BEGIN RETURN stack[ext_fp - i] END ReadValue;

PROCEDURE ReadInt(i: CARDINAL; VAR err: BOOLEAN): INTEGER =
  BEGIN
    TYPECASE stack[ext_fp - i] OF
      NULL => (* SKIP *)
    | RTVal.Number (n) => RETURN ROUND(n.val)
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN 0
  END ReadInt;

PROCEDURE ReadReal(i: CARDINAL; VAR err: BOOLEAN): JunoValue.Real =
  BEGIN
    TYPECASE stack[ext_fp - i] OF
      NULL => (* SKIP *)
    | RTVal.Number (n) => RETURN n.val
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN 0.0
  END ReadReal;

PROCEDURE ReadText(i: CARDINAL; VAR err: BOOLEAN): TEXT =
  BEGIN
    TYPECASE stack[ext_fp - i] OF
      NULL => (* SKIP *)
    | RTVal.Text (t) => RETURN t.val
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN NIL
  END ReadText;

PROCEDURE ReadPair(i: CARDINAL; VAR err: BOOLEAN): RTVal.Pair =
  BEGIN
    TYPECASE stack[ext_fp - i] OF
      NULL => (* SKIP *)
    | RTVal.Pair (p) => RETURN p
    ELSE (* SKIP *)
    END;
    err := TRUE;
    RETURN NIL
  END ReadPair;

PROCEDURE WriteValue(i: CARDINAL; val: RTVal.T) =
  BEGIN stack[ext_fp - i] := val END WriteValue;

PROCEDURE WriteInt(i: CARDINAL; int: INTEGER) =
  BEGIN stack[ext_fp - i] := RTVal.FromInt(int) END WriteInt;

PROCEDURE WriteReal(i: CARDINAL; r: JunoValue.Real) =
  BEGIN stack[ext_fp - i] := RTVal.FromReal(r) END WriteReal;

PROCEDURE WriteText(i: CARDINAL; t: TEXT) =
  BEGIN stack[ext_fp - i] := RTVal.FromText(t) END WriteText;

PROCEDURE PushValue(v: RTVal.T) =
  <* FATAL StackOverflow, PushedNIL *>
  BEGIN Push(v) END PushValue;

VAR (* CONST *)
  emptyFrame := NEW(Frame, downF := NIL, upF := NIL, fp := BaseFP);

PROCEDURE ResetMachine() =
  BEGIN
    sp := 0;
    fp := BaseFP;
    pc := PC{InitialProc, 0};
    baseFrame := emptyFrame;
    topFrame := baseFrame
  END ResetMachine;

PROCEDURE Save() =
  BEGIN
    saved_fp := fp;
    saved_sp := sp;
    saved_cond := cond;
    saved_pc := pc;
    saved_stack := NEW(REF ARRAY OF StackValue, NUMBER(stack^));
    saved_stack^ := stack^
  END Save;

PROCEDURE Restore() =
  BEGIN
    fp := saved_fp;
    sp := saved_sp;
    cond := saved_cond;
    pc := saved_pc;
    stack := NEW(REF ARRAY OF StackValue, NUMBER(saved_stack^));
    stack^ := saved_stack^
  END Restore;

PROCEDURE GetStackSize(): CARDINAL =
  BEGIN
    RETURN stackSize
  END GetStackSize;

PROCEDURE EnlargeStack() =
  VAR newStack := NEW(REF ARRAY OF StackValue, NUMBER(stack^) * 2); BEGIN
    SUBARRAY(newStack^, 0, NUMBER(stack^)) := stack^;
    stack := newStack;
    stackSize := NUMBER(stack^)
  END EnlargeStack;

TYPE
  Point = RECORD x, y: Real END;
  Segment = RECORD a, b: Point END;

PROCEDURE ExtractSegment(seg: RTVal.T; VAR (* OUT *) out: Segment):
    BOOLEAN =

If seg is a pair of points, then set out to contain the four coordinates and return FALSE. Otherwise, return TRUE.

  BEGIN
    TYPECASE seg OF
    | NULL => RETURN TRUE
    | RTVal.Pair (p) =>
        IF ExtractPoint(p.car, out.a) THEN RETURN TRUE END;
        IF ExtractPoint(p.cdr, out.b) THEN RETURN TRUE END;
    ELSE RETURN TRUE
    END;
    RETURN FALSE
  END ExtractSegment;

PROCEDURE ExtractPoint(pt: RTVal.T; VAR (* OUT *) out: Point): BOOLEAN =

If pt is a pair of real numbers, then set out to contain its coordinates and return FALSE. Otherwise, return TRUE.

  BEGIN
    TYPECASE pt OF
    | NULL => RETURN TRUE
    | RTVal.Pair (p) =>
        IF ExtractReal(p.car, out.x) THEN RETURN TRUE END;
        IF ExtractReal(p.cdr, out.y) THEN RETURN TRUE END;
    ELSE RETURN TRUE
    END;
    RETURN FALSE
  END ExtractPoint;

PROCEDURE ExtractReal(r: RTVal.T; VAR (* OUT *) out: Real): BOOLEAN =

If r is a number, set out to its value and return FALSE. Otherwise, return TRUE.

  BEGIN
    TYPECASE r OF
    | NULL => RETURN TRUE
    | RTVal.Number (v) => out := v.val
    ELSE RETURN TRUE
    END;
    RETURN FALSE
  END ExtractReal;

PROCEDURE AppendClosure(l1, l2: RTVal.T): RTVal.T =

Return the result of appending the list l2 to the end of the closure l1, or NIL if l1 is not a list.

  BEGIN
    IF ListLen(l1) = -1
      THEN RETURN NIL
      ELSE RETURN Append(l1, l2)
    END
  END AppendClosure;

PROCEDURE ListLen(t: RTVal.T): INTEGER =

Returns the length of the list t, or -1 if t is not a list.

  VAR res := 0; BEGIN
    LOOP
      TYPECASE t OF
      | NULL => EXIT
      | RTVal.Pair (p) =>
        INC(res);
        t := p.cdr
      ELSE EXIT
      END
    END;
    IF t = RTVal.nil
      THEN RETURN res
      ELSE RETURN -1
    END
  END ListLen;

PROCEDURE Append(l1, l2: RTVal.T): RTVal.T =

Requires l1 and l2 to be lists; returns the result of appending them.

  BEGIN
    TYPECASE l1 OF <* NOWARN *>
      RTVal.Null => RETURN l2
    | RTVal.Pair (p) =>
        RETURN RTVal.FromPair(p.car, Append(p.cdr, l2))
    END
  END Append;

VAR
  machine := NEW(MUTEX);
  isRunning := FALSE;
  intPending := FALSE;
  intSeen := NEW(Thread.Condition);

PROCEDURE Interrupt() =

Send an interrupt; block until the machine signals that the interrupt has been seen.

  BEGIN
    LOCK machine DO
      IF NOT isRunning THEN RETURN END;
      intPending := TRUE;
      WHILE intPending DO Thread.Wait(machine, intSeen) END
    END
  END Interrupt;

VAR instrCount: INTEGER;

PROCEDURE EtpLogExecStep(<*UNUSED*> bc: ByteCode) =
  BEGIN END EtpLogExecStep;

PROCEDURE EtpLogExecInstrCount(<*UNUSED*> cnt: INTEGER) =
  BEGIN END EtpLogExecInstrCount;

PROCEDURE Exec(): ExecRes =
  VAR
    a: BytePtr := ADR(code_tbl[pc.proc][pc.offset]);
    bc: ByteCode;
    offset: JunoMarshal.Short;
    index, extSlot: CARDINAL;
    a_init: BytePtr;
    (* "a_init" always contains the value "a" had at the beginning of the
       instruction, so that the instruction can be restarted in case of a
       stack overflow.  See the "EXCEPT" clause below. *)
    a_ut: BytePtr;
    (* "a_ut" is the address of the most recent instruction that branches
       to its offset because one of its argument is an undefined term *)

  PROCEDURE HandleError(ec: JunoRTError.Code): ExecRes =
  (* Return a "ExecRes" in the "TrapCode.Error" case with error code "ec". On
     entry to this routine, "a" should be pointing to the first byte of the
     instruction just after the one causing the error. *)
    VAR startLoc := ADR(code_tbl[pc.proc][0]); eLoc: PC; BEGIN
      pc.offset := a - startLoc;
      IF ec = JunoRTError.Code.UndefTerm
        THEN eLoc := PC{pc.proc, a_ut - startLoc}
        ELSE eLoc := PC{pc.proc, a_init - startLoc}
      END;
      RecomputeFrames();
      RETURN ExecRes{TrapCode.Error, eLoc, extSlot, ec}
    END HandleError;

  PROCEDURE HandleIntr(): ExecRes =
  <* SPEC machine IN LL *>
    BEGIN
      intPending := FALSE;
      Thread.Broadcast(intSeen);
      pc.offset := a - ADR(code_tbl[pc.proc][0]);
      RecomputeFrames();
      RETURN ExecRes{TrapCode.Interrupt, pc, extSlot, NoErrorCode}
    END HandleIntr;

  PROCEDURE MkName(m, n: Atom.T): TEXT =
    VAR res := Atom.ToText(n); BEGIN
      IF m # NIL THEN res := Atom.ToText(m) & "." & res END;
      RETURN res
    END MkName;

  PROCEDURE MakeClosure(s: INTEGER) RAISES {StackOverflow}=
  (* Push an empty closure for slot "s" *)
    <* FATAL PushedNIL *>
    VAR nm: TEXT; BEGIN
      IF s > 0
        THEN nm := MkName(procAttrs[s].modName, procAttrs[s].name)
        ELSE nm := MkName(extProcAttrs[-s].modName, extProcAttrs[-s].name)
      END;
      Push(RTVal.FromPair(
        RTVal.FromPair(RTVal.FromText(nm), RTVal.FromInt(s)),
        RTVal.nil))
    END MakeClosure;

  PROCEDURE DoCall(slot: CARDINAL) RAISES {StackOverflow} =
    <* FATAL PushedNIL *>
    VAR
      firstaddr := ADR(code_tbl[pc.proc][0]);
      iS := MakeCallState(
        pc := PC{proc := pc.proc, offset := a - firstaddr},
        fp := fp);
    BEGIN
      Push(iS);
      fp := sp - 1;   (* Do this here in case "Push" fails *)
      pc.proc := slot;
      pc.offset := 0;
      a := ADR(code_tbl[slot][0]);
      WITH sig = procAttrs[slot].sig DO
        IF sig.outs = 0 AND sig.inouts = 0 THEN
          RTVal.Mark()
        END
      END
    END DoCall;

  PROCEDURE DoExtCall(slot: CARDINAL) =
    BEGIN
      ext_fp := sp;
      extSlot := slot;
      cond := ext_code_tbl[slot].invoke();
    END DoExtCall;

  (* Exec *)
  BEGIN
   instrCount := 0;
   LOCK machine DO
     <* ASSERT NOT isRunning *>
     isRunning := TRUE
   END;
   TRY
    IF pc.proc = InitialProc THEN
      RecomputeFrames();
      RETURN ExecRes{TrapCode.NormalHalt, NoTrapLoc, 0, NoErrorCode}
    END;
    TRY
      LOOP
        a_init := a;
        bc := a^;
        INC(a);
        EtpLogExecStep(bc); INC(instrCount);
        CASE bc OF
        | BC.PUSHL =>
            offset := JunoMarshal.ReadShort(a);
            Push(stack[fp + offset])
        | BC.POPL =>
            offset := JunoMarshal.ReadShort(a);
            stack[fp + offset] := Pop()
        | BC.PUSHG =>
            index := JunoMarshal.ReadULong(a);
            Push(RTVal.FromJV(value_tbl[index]))
        | BC.POPG =>
            index := JunoMarshal.ReadULong(a);
            value_tbl[index] := RTVal.ToJV(Pop())
        | BC.INCSP =>
            IF sp + a^ >= stackSize THEN RAISE StackOverflow END;
            INC(sp, a^);
            INC(a)
        | BC.DECSP =>
            DEC(sp, a^); INC(a)
        | BC.PUSHM3NIL =>
            IF sp + a^ >= stackSize THEN RAISE StackOverflow END;
            FOR i := 1 TO a^ DO stack[sp] := NIL; INC(sp) END;
            INC(a)
        | BC.PUSHNIL =>
            Push(RTVal.nil)
        | BC.PUSHNUM =>
            Push(RTVal.FromReal(JunoMarshal.ReadReal(a)))
        | BC.C_OFF =>
            cond := FALSE
        | BC.C_ON =>
            cond := TRUE
        | BC.JUMP =>
            offset := JunoMarshal.ReadShort(a);
            IF offset <= 0 THEN
              LOCK machine DO
                IF intPending THEN RETURN HandleIntr() END
              END
            END;
            INC(a, offset)
        | BC.TJUMP =>
            offset := JunoMarshal.ReadShort(a);
            IF cond THEN INC(a, offset) END
        | BC.FJUMP =>
            offset := JunoMarshal.ReadShort(a);
            IF NOT cond THEN INC(a, offset) END
        | BC.UJUMP =>
            offset := JunoMarshal.ReadShort(a);
            IF NOT cond THEN
              DEC(sp);			 (* skip past single OUT parameter *)
              a_ut := a_init;		 (* set "undef term" address *)
              INC(a, offset)
            END
        | BC.CALL =>
            LOCK machine DO
              IF intPending THEN
                RETURN HandleIntr()
              END
            END;
            DoCall(JunoMarshal.ReadULong(a))
        | BC.CALLEXT =>
            DEC(instrCount);
            DoExtCall(JunoMarshal.ReadULong(a));
            IF NOT cond THEN
              RETURN HandleError(JunoRTError.Code.FailedExtProc)
            END
        | BC.RET =>
            WITH sig = procAttrs[pc.proc].sig DO
              IF sig.outs = 0 AND sig.inouts = 0 THEN
                RTVal.Dispose()
              END
            END;
            sp := fp + 1;
            VAR s: CallState := Pop(); BEGIN
              pc := s.pc;
              fp := s.fp;
              DisposeCallState(s)
            END;
            IF pc.proc = InitialProc THEN
              RecomputeFrames();
              RETURN ExecRes{TrapCode.NormalHalt, NoTrapLoc, 0, NoErrorCode}
            END;
            a := ADR(code_tbl[pc.proc][pc.offset])
        | BC.ERROR =>
            VAR ec := a^; BEGIN
              INC(a); RETURN HandleError(VAL(ec, JunoRTError.Code))
            END
        | BC.FERROR =>
            IF cond THEN INC(a) ELSE
              VAR ec := a^; BEGIN
                INC(a); RETURN HandleError(VAL(ec, JunoRTError.Code))
              END
            END
        | BC.ADD =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(t1 + t2))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.SUBTRACT =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(t1 - t2))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.MULTIPLY =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(t1 * t2))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.DIVIDE =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err AND t2 # 0.0
                THEN Push(RTVal.FromReal(t1 / t2))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.DIV_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err AND t2 # 0.0
                THEN Push(RTVal.FromInt(FLOOR(t1 / t2)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.MOD_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err AND t2 # 0.0
                THEN Push(RTVal.FromReal(t1 MOD t2))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.NEGATE =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(-t1))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.ABS_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(ABS(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.FLOOR_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromInt(FLOOR(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.CEILING_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromInt(CEILING(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.ROUND_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromInt(ROUND(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.MAX_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(MAX(t1, t2)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.MIN_ =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(MIN(t1, t2)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.ATAN =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(JunoValue.Atan(t1, t2)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.SIN =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(JunoValue.Sin(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.COS =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(JunoValue.Cos(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.LN =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(JunoValue.Ln(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.EXP =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t1 := PopNum(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromReal(JunoValue.Exp(t1)))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.REL =>           (* Evaluate (x, y) REL ((ax, ay), (bx, by)) *)
            offset := JunoMarshal.ReadShort(a);
            VAR t2, t1 := Pop(); p: Point; s: Segment; BEGIN
              IF ExtractPoint(t1, p) OR ExtractSegment(t2, s) THEN
                a_ut := a_init;
                INC(a, offset)
              ELSE
                WITH a = s.a, b = s.b DO
                  Push(RTVal.FromPair(
                    RTVal.FromReal(a.x + (b.x-a.x)*p.x - (b.y-a.y)*p.y),
                    RTVal.FromReal(a.y + (b.x-a.x)*p.y + (b.y-a.y)*p.x)))
                END
              END
            END
        | BC.CAR =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; pr := PopPair(err); BEGIN
              IF NOT err
                THEN Push(pr.car)
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.CDR =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; pr := PopPair(err); BEGIN
              IF NOT err
                THEN Push(pr.cdr)
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.CAR_CDR =>
            offset := JunoMarshal.ReadShort(a);
            (* This is the only place we test "sp" because this is the
               only bytecode that pops stuff off the stack and pushes
               even more stuff back *)
            IF sp = stackSize THEN
              VAR err := FALSE; pr := PopPair(err); BEGIN
            	IF NOT err
            	  THEN Push(pr.cdr); Push(pr.car)
            	  ELSE a_ut := a_init; INC(a, offset)
            	END
              END
            ELSE
              RAISE StackOverflow
            END
        | BC.CONS =>
            VAR t2, t1 := Pop(); BEGIN
              Push(RTVal.FromPair(t1, t2))
            END
        | BC.LIST =>
            Push(PopList(JunoMarshal.ReadUShort(a)))
        | BC.CONCAT =>
            offset := JunoMarshal.ReadShort(a);
            VAR err := FALSE; t2, t1 := PopText(err); BEGIN
              IF NOT err
                THEN Push(RTVal.FromText(t1 & t2))
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.IS_REAL =>
            VAR t := stack[sp - 1]; BEGIN
              cond := t # NIL AND ISTYPE(t, RTVal.Number)
            END
        | BC.IS_INT =>
            TYPECASE stack[sp - 1] OF
              NULL => cond := FALSE
            | RTVal.Number (n) => cond := (n.val = FLOAT(ROUND(n.val)))
            ELSE cond := FALSE
            END
        | BC.IS_TEXT =>
            VAR t := stack[sp - 1]; BEGIN
              cond := t # NIL AND ISTYPE(t, RTVal.Text)
            END
        | BC.IS_PAIR =>
            VAR t := stack[sp - 1]; BEGIN
              cond := t # NIL AND ISTYPE(t, RTVal.Pair)
            END
        | BC.EQUAL =>
            VAR t2, t1 := Pop(); BEGIN
              cond := RTVal.Equal(t1, t2)
            END
        | BC.LESS =>
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              cond := (NOT err) AND (t1 < t2)
            END
        | BC.AT_MOST =>
            VAR err := FALSE; t2, t1 := PopNum(err); BEGIN
              cond := (NOT err) AND (t1 <= t2)
            END
        | BC.CONG =>
            VAR t2, t1 := Pop(); s1, s2: Segment; BEGIN
              IF ExtractSegment(t1, s1) OR ExtractSegment(t2, s2) THEN
                cond := FALSE
              ELSE
                PROCEDURE LenSq(READONLY s: Segment): Real =
                  VAR dx := s.b.x - s.a.x; dy := s.b.y - s.a.y; BEGIN
                    RETURN dx * dx + dy * dy
                  END LenSq;
                CONST Epsilon = 2.0E-3;
                VAR len1 := LenSq(s1); len2 := LenSq(s2); BEGIN
                  cond := ABS(len2 - len1) < Epsilon
                END
              END
            END
        | BC.PARA =>
            VAR t2, t1 := Pop(); s1, s2: Segment; BEGIN
              IF ExtractSegment(t1, s1) OR ExtractSegment(t2, s2) THEN
                cond := FALSE
              ELSE
                CONST Epsilon = 1.0E-4;
                VAR
                  dx1 := s1.b.x - s1.a.x; dy1 := s1.b.y - s1.a.y;
                  dx2 := s2.b.x - s2.a.x; dy2 := s2.b.y - s2.a.y;
                BEGIN
                  cond := ABS(dx2 * dy1 - dx1 * dy2) < Epsilon
                END
              END
            END
        | BC.HOR =>
            VAR t2, t1 := Pop(); p1, p2: Point; BEGIN
              IF ExtractPoint(t1, p1) OR ExtractPoint(t2, p2)
                THEN cond := FALSE
                ELSE cond := p1.y = p2.y
              END
            END
        | BC.VER =>
            VAR t2, t1 := Pop(); p1, p2: Point; BEGIN
              IF ExtractPoint(t1, p1) OR ExtractPoint(t2, p2)
                THEN cond := FALSE
                ELSE cond := p1.x = p2.x
              END
            END
        | BC.NEWCL =>    MakeClosure(JunoMarshal.ReadULong(a))
        | BC.NEWEXTCL => MakeClosure(-JunoMarshal.ReadULong(a))
        | BC.CLOSE =>
            VAR
              l := PopList(JunoMarshal.ReadUShort(a));
              cl := Pop();
              offset := JunoMarshal.ReadShort(a);
            BEGIN
              cl := AppendClosure(cl, l);
              IF cl # NIL
                THEN Push(cl)
                ELSE a_ut := a_init; INC(a, offset)
              END
            END
        | BC.APPLY =>
            VAR
              outs := JunoMarshal.ReadUShort(a);
              inouts := JunoMarshal.ReadUShort(a);
              ins := JunoMarshal.ReadUShort(a);
              offset := JunoMarshal.ReadShort(a);
              clRec := UnpackClosure(Pop());
            BEGIN
              IF clRec.valid AND ins + clRec.argsLen = clRec.sig.ins
                 AND outs = clRec.sig.outs AND inouts = clRec.sig.inouts THEN
                NARROW(stack[fp], CallState).clIns := clRec.argsLen;
                InsertList(clRec.args, clRec.argsLen, ins);
                IF clRec.slot > 0 THEN
                  DoCall(clRec.slot)
                ELSE
                  DoExtCall(-clRec.slot);
                  IF NOT cond THEN
                    RETURN HandleError(JunoRTError.Code.FailedExtProc)
                  END
                END
              ELSE
                a_ut := a_init;
                INC(a, offset)
              END
            END
        | BC.CLDECSP =>
            DEC(sp, NARROW(stack[fp], CallState).clIns)
        | BC.SOLVE =>
            DEC(instrCount);
            DoSolve(a)
        ELSE
            Wr.PutText(stderr, "Fatal error in JunoRT.Exec:\n");
            Wr.PutText(stderr, "  Unknown byte code " & Fmt.Int(bc) & "\n");
            pc.offset := a_init - ADR(code_tbl[pc.proc][0]);
            Wr.PutText(stderr, "  PC = [" & PCToProcName(pc)
              & ", " & Fmt.Int(pc.offset) & "]\n\n");
            Wr.PutText(stderr, "Procedure disassembly:\n");
            Wr.Flush(stderr);
            JunoDisassem.P(code_tbl[pc.proc], stderr);
            Wr.Flush(stderr);
            <* ASSERT FALSE *>
        END
      END
    EXCEPT
    | StackOverflow =>
        pc.offset := a_init - ADR(code_tbl[pc.proc][0]);
        RecomputeFrames();
        RETURN ExecRes{TrapCode.StackOverflow, pc, 0, NoErrorCode}
    | PushedNIL =>
        RETURN HandleError(JunoRTError.Code.UsedUninitialized)
    END
   FINALLY
    LOCK machine DO
      isRunning := FALSE
    END;
    EtpLogExecInstrCount(instrCount);
    RTVal.Dispose()
   END
  END Exec;

TYPE
  ClosureRec = RECORD
    valid: BOOLEAN;
    slot: INTEGER;
    args: JunoValue.T;
    argsLen: CARDINAL;
    sig: Sig;
  END;

PROCEDURE UnpackClosure(cl: RTVal.T): ClosureRec =
  VAR res: ClosureRec; BEGIN
    TYPECASE cl OF RTVal.Pair (p) =>
      TYPECASE p.car OF RTVal.Pair (q) =>
        TYPECASE q.cdr OF RTVal.Number (s) =>
          res.slot := ROUND(s.val);
          IF (res.slot > 0 AND res.slot < next_code_idx) THEN
            res.sig := procAttrs[res.slot].sig
          ELSIF res.slot <= 0 AND -res.slot < next_ext_idx THEN
            res.sig := extProcAttrs[-res.slot].sig
          ELSE
            res.valid := FALSE; RETURN res
          END;
          res.argsLen := ListLen(p.cdr);
          IF res.argsLen >= 0 THEN
            res.args := p.cdr;
            res.valid := TRUE;
            RETURN res
          END
        ELSE (*SKIP*)
        END
      ELSE (*SKIP*)
      END
    ELSE (*SKIP*)
    END;
    res.valid := FALSE;
    RETURN res
  END UnpackClosure;

PROCEDURE ExecFromSlot(slot: CARDINAL; reset := TRUE): ExecRes =
  BEGIN
    IF reset THEN ResetMachine() END;
    PushFrame(PC{slot, 0}, size := 0);
    RETURN Exec()
  END ExecFromSlot;

PROCEDURE AttrsToProcName(READONLY p: ProcAttr): TEXT =
  VAR res := Atom.ToText(p.name); BEGIN
    IF p.modName # NIL THEN res := Atom.ToText(p.modName) & "." & res END;
    RETURN res
  END AttrsToProcName;

PROCEDURE PCToProcName(READONLY pc: PC): TEXT =
  BEGIN RETURN AttrsToProcName(procAttrs[pc.proc]) END PCToProcName;

PROCEDURE ExtSlotToProcName(slot: CARDINAL): TEXT =
  BEGIN RETURN AttrsToProcName(extProcAttrs[slot]) END ExtSlotToProcName;

PROCEDURE RunTimeError(READONLY execRes: ExecRes): TEXT =
  BEGIN
    IF execRes.errorCode = JunoRTError.Code.FailedExtProc THEN
      RETURN "Built-in procedure \"" & ExtSlotToProcName(execRes.extSlot)
        & "\" failed"
    ELSE
      RETURN JunoRTError.names[execRes.errorCode]
    END
  END RunTimeError;

PROCEDURE TrapMessage(READONLY execRes: ExecRes): TEXT =
  PROCEDURE Msg(prefix: TEXT; READONLY eRes: ExecRes): TEXT =
    BEGIN RETURN prefix & " in \"" & PCToProcName(eRes.trapLoc) & "\"" END Msg;
  BEGIN
    CASE execRes.trapCode OF
      TrapCode.NormalHalt =>    RETURN "Execution completed successfully"
    | TrapCode.BreakPoint =>    RETURN Msg("Hit breakpoint", execRes)
    | TrapCode.Interrupt =>     RETURN Msg("Juno stopped", execRes)
    | TrapCode.StackOverflow => RETURN Msg("Stack Overflow", execRes)
    | TrapCode.Error =>
        RETURN Msg("Run-time error", execRes)
          & ":\n" & RunTimeError(execRes)
    END
  END TrapMessage;

VAR
  con := NEW(JunoSolve.Constraints, 100);
  var := NEW(JunoSolve.Vars, 100);

PROCEDURE DoSolve(VAR a: BytePtr) =
  VAR
    inouts := JunoMarshal.ReadUShort(a);
    ins := JunoMarshal.ReadUShort(a);
    nc := JunoMarshal.ReadUShort(a);
    nv := ins + inouts;
    params: CARDINAL := sp - nv;
    c: CARDINAL := 0;
  BEGIN
    (* check that "con" and "var" are large enough *)
    IF NUMBER(con^) < nc THEN
      con := NEW(JunoSolve.Constraints, MAX(nc, 2 * NUMBER(con^)))
    END;
    IF NUMBER(var^) < nv THEN
      var := NEW(JunoSolve.Vars, MAX(nv, 2 * NUMBER(var^)))
    END;

    (* create variables *)
    FOR i := 0 TO nv - 1 DO
      var[i] := JunoSolve.New(
        known := (i >= inouts),
        val := stack[params + i])
    END;

    (* process constraints *)
    WHILE c < nc DO
      VAR n: BC.ConRange := a^; x, y, z: JunoMarshal.Short := 0; BEGIN
        INC(a);
        x := JunoMarshal.ReadUShort(a);
        IF n < BC.REAL_C  THEN y := JunoMarshal.ReadUShort(a) END;
        IF n < BC.EQUAL_C THEN z := JunoMarshal.ReadUShort(a) END;
        CASE n OF
        | BC.CONS_C => con[c] := JunoSolve.NewCons(var[x], var[y], var[z])
        | BC.SUM_C =>  con[c] := JunoSolve.NewPlus(var[x], var[y], var[z])
        | BC.PROD_C => con[c] := JunoSolve.NewTimes(var[x], var[y], var[z])
        | BC.ATAN_C => con[c] := JunoSolve.NewAtan(var[x], var[y], var[z])
        | BC.EQUAL_C =>con[c] := JunoSolve.NewEqual(var[x], var[y])
        | BC.SIN_C =>  con[c] := JunoSolve.NewSin(var[x], var[y])
        | BC.COS_C =>  con[c] := JunoSolve.NewCos(var[x], var[y])
        | BC.EXP_C =>  con[c] := JunoSolve.NewExp(var[x], var[y])
        | BC.REAL_C => con[c] := JunoSolve.NewReal(var[x])
        | BC.TEXT_C => con[c] := JunoSolve.NewText(var[x])
        END;
        INC(c)
      END
    END;

    (* solve constraints *)
    cond := JunoSolve.P(SUBARRAY(con^, 0, nc));

    (* if successful, store results on the stack *)
    IF cond THEN
      FOR i := 0 TO inouts - 1 DO
        stack[params + i] := var[i].val
      END
    END;
    JunoSolve.Dispose();
    sp := sp - ins
  END DoSolve;

VAR csAvail: CallState := NIL;

PROCEDURE MakeCallState(pc: PC; fp: CARDINAL): CallState =
  VAR res: CallState; BEGIN
    IF csAvail = NIL THEN
      res := NEW(CallState)
    ELSE
      res := csAvail;
      csAvail := csAvail.nextAvail
    END;
    res.pc := pc;
    res.fp := fp;
    RETURN res
  END MakeCallState;

PROCEDURE DisposeCallState(st: CallState) =
  BEGIN
    st.nextAvail := csAvail;
    csAvail := st
  END DisposeCallState;

BEGIN
  value_tbl := NEW(REF ARRAY OF JunoValue.T, 1000);
  code_tbl := NEW(REF ARRAY OF ByteStream, 1000);
  procAttrs := NEW(REF ARRAY OF ProcAttr, 1000);
  ext_code_tbl := NEW(REF ARRAY OF ExternalCode, 100);
  extProcAttrs := NEW(REF ARRAY OF ProcAttr, 100);
  ResetMachine()
END JunoRT.