RISC virtual machine by Niklaus Wirth from his book, Compiler Construction. (This is actually oberon, not pascal, but github doesn't highlight oberon)

risc.pas

MODULE RISC; (* NW 22.9.07 / 28.3.11 *)
IMPORT SYSTEM, Texts, Oberon;     


CONST
   MemSize = 1024;    (* in words *)
   MOV = 0; AND = 1; IOR = 2;  XOR = 3;  LSL = 4; ASR = 5;
   ADD = 8; SUB = 9; MUL = 10; Div = 11; CMP = 12;


VAR
   IR   : LONGINT;  (* instruction register *)
   PC   : LONGINT;  (* program counter *)
   N, Z : BOOLEAN;  (* condition regosters *)
   R    : ARRAY 16 OF LONGINT;


PROCEDURE Execute*( VAR M: ARRAY OF LONGINT; VAR S: Texts.Scanner; VAR W: Texts.Writer );
   VAR pq, a, b, op, im : LONGINT;     (* instruction fields *)
   VAR adr, A, B, C     : LONGINT;
BEGIN

   PC := 0;
   REPEAT                              (* interpretation cycle *)
      
      IR := M[ PC ];
      INC( PC );
      
      pq := IR DIV 40000000H MOD 4;    (* insr. class *)
      a :=  IR DIV 1000000H MOD 10H;
      b :=  IR DIV 100000H MOD 10H;
      op := IR DIV 10000H MOD 10H;
      im := IR MOD 10000H;
      
      CASE pq OF

	0, 1 :                         (* register instructions *)
	 B := R[ b ];
	 IF pq = 0 THEN
            C := R[ IR MOD 10H ]
	 ELSIF ODD( IR DIV 10000000H ) THEN
            C := im + 0FFFF0000H
	 ELSE
            C := im
	 END ;
         
	 CASE op OF
	   MOV      : A := C
         | AND      : A := SYSTEM.VAL( LONGINT, SYSTEM.VAL( SET, B ) * SYSTEM.VAL( SET, C ))
         | IOR      : A := SYSTEM.VAL( LONGINT, SYSTEM.VAL( SET, B ) + SYSTEM.VAL( SET, C ))
         | XOR      : A := SYSTEM.VAL( LONGINT, SYSTEM.VAL( SET, B ) / SYSTEM.VAL( SET, C ))
         | LSL      : A := SYSTEM.LSH( B, C )
         | ASR      : IF ODD( IR DIV 20000000H ) THEN A := SYSTEM.ROT( B, -C ) ELSE A := ASH( B, -C ) END
         | ADD      : A := B + C
         | SUB, CMP : A := B - C
         | MUL      : A := B * C
         | Div      : A := B DIV C
	 END ;
         
	 IF op # CMP THEN
            R[ a ] := A 
         END ;
         
	 N := A < 0; 
         Z := A = 0

      | 2 : (* memory instructions *)
         
	 adr := ( R[ b ] + IR ) MOD 100000H DIV 4;
	 IF adr < MemSize THEN
	    IF ODD( IR DIV 20000000H ) THEN
               M[ adr ] := R[ a ] 
            ELSE
               R[ a ] := M[ adr ]
            END
	 ELSE (* I/O *)
	    IF ODD( IR DIV 20000000H ) THEN
	       IF adr = 3FFF2H THEN
                  Texts.WriteInt( W, R[ a ], 8 )
	       ELSIF adr = 3FFF3H THEN
                  Texts.WriteLn( W );
                  Texts.Append( Oberon.Log, W.buf ) 
	       END
	    ELSE 
	       IF adr = 3FFF2H THEN 
                  Texts.Scan( S );
                  R[ a ] := S.i 
	       ELSIF adr = 3FFF3H THEN
		  IF S.class # Texts.Int THEN
                     R[ a ] := 1 
                  ELSE
                     R[ a ] := 0 
                  END
	       END
	    END
	 END ;
         
      | 3 : (* branch instructions *)
	 IF ( a = 0 ) & N
         OR ( a = 1 ) & Z
         OR ( a = 5 ) & N 
         OR ( a = 6 ) & ( N OR Z ) 
         OR ( a = 7 ) 
         OR ( a = 8 ) & ~N 
         OR ( a = 9 ) & ~Z 
         OR ( a = 13 ) & ~N
         OR ( a = 14 ) & ~( N OR Z ) THEN
	    IF ODD( IR DIV 10000000H ) THEN
               R[ 15 ] := PC * 4
            END ;
	    IF ODD( IR DIV 20000000H ) THEN 
               PC := ( PC + ( IR MOD 1000000H )) MOD 40000H
	    ELSE 
               PC := R[ IR MOD 10H ] DIV 4
	    END
	 END
      END ;
      
      Texts.Append( Oberon.Log, W.buf )
      
   UNTIL PC = 0
END Execute;


END RISC.

Please anyone with codes of c++,since the one here is pascal....Please help