DCL (T(10)) FIXED BIN(31); /* scratch space of length N/2 */

MERGE: PROCEDURE (A,LA,B,LB,C);
   DECLARE (A(*),B(*),C(*)) FIXED BIN(31);
   DECLARE (LA,LB) FIXED BIN(31) NONASGN;
   DECLARE (I,J,K) FIXED BIN(31);

   I=1; J=1; K=1;
   DO WHILE ((I <= LA) & (J <= LB));
      IF(A(I) <= B(J)) THEN
         DO; C(K)=A(I); K=K+1; I=I+1; END;
      ELSE
         DO; C(K)=B(J); K=K+1; J=J+1; END;
   END;
   DO WHILE (I <= LA);
      C(K)=A(I); I=I+1; K=K+1;
   END;
   RETURN;
END MERGE;

MERGESORT: PROCEDURE (A,N) RECURSIVE ;
     DECLARE (A(*))               FIXED BINARY(31);
     DECLARE N                    FIXED BINARY(31) NONASGN;
     DECLARE Temp                 FIXED BINARY;
     DECLARE (M,I)                FIXED BINARY;
     DECLARE AMP1(N)              FIXED BINARY(31) BASED(P);
     DECLARE P POINTER;
    IF (N=1) THEN RETURN;
   M = trunc((N+1)/2);
   IF (M>1) THEN CALL MERGESORT(A,M);
   P=ADDR(A(M+1));
   IF (N-M > 1) THEN CALL MERGESORT(AMP1,N-M);
   IF A(M) <= AMP1(1) THEN RETURN;
   DO I=1 to M; T(I)=A(I); END;
   CALL MERGE(T,M,AMP1,N-M,A);
   RETURN;
END MERGESORT;