SUBROUTINE INSERT
C
C	PURPOSE: INSERTS A NOP (-2) INSTRUCTION INTO PROGRAM MEMORY, MOVING
C	 REMAINING PROGRAM STEPS DOWN.  NOTE: INSERT LEAVES PC POINTING AT
C	 NOP COMMAND AND WILL CHECK TO MAKE SURE THAT INSERTION WILL NOT
C	 REMOVE A FINAL R/S (0) COMMAND FROM LAST PROGRAM STEP, P(NSTEPS).
C
C	VARIABLES:
C	 P	-COMMON BYTE ARRAY CONTAINING PROGRAM STEPS
C	 PC	-COMMON INTEGER VARIABLE POINTING TO CURRENT COMMAND
C	 ERROR	-COMMON BYTE FLAG TO INDICATE ERROR CONDITION
C	 NSTEPS	-LOCAL VARIABLE SET TO CURRENT # PROGRAM STEPS
C	 NOP	-LOCAL BYTE VARIABLE SET TO NOP COMMAND CODE (-2)
C	 RS	-LOCAL BYTE VARIABLE SET TO R/S COMMAND CODE (0)
C
C
C
C	SORENSON, 1/81
C
	COMMON/FLAGS/STATE,ERROR,STKLFT,NEST,ANGLES,RADIX,DIGITS,FLAG(4)
	BYTE STATE,ERROR,STKLFT,NEST,ANGLES,RADIX,DIGITS,FLAG
	COMMON/MEMORY/PC,P(1000)
	BYTE P
	INTEGER PC
	BYTE NOP,RS
	DATA NSTEPS/1000/,NOP/-2/,RS/0/
C
C	CHECK TO MAKE SURE R/S INSTRUCTION WILL STILL BE IN LAST PROGRAM STEP
C
	IF(P(NSTEPS-1).EQ.RS)GO TO 5
C
C	FLAG ERROR= INSUFFICIENT PROGRAM SPACE
C
	ERROR=-1
	RETURN
C
C	MOVE ALL PROGRAM STEPS DOWN BY 1 LOCATION
C
5	J=NSTEPS
	DO 10 I=PC,NSTEPS-1
	P(J)=P(J-1)
	J=J-1
10	CONTINUE
C
C	SET CURRENT PROGRAM STEP TO NOP INSTRUCTION AND EXIT
C
	P(PC)=NOP
	RETURN
	END