ADD	HL,DE	Reform the old value of
		EX	DE,HL	STKEND and pass it to DE
		RET		before returning.

THE 'COLLECT A LINE NUMBER' SUBROUTINE
On entry the HL register pair points to the location under consideration.  If the location holds a value that constitutes a suitable high byte for a line number then the line number is returned in DE.  However if this is not so then the location addressed by DE is tried instead; and should this also be unsuccessful line number zero is returned.

168F	LINE-ZERO	DEFB	+00	Line number zero.
		DEFB	+00	
1961	LINE-NO-A	EX	DE,HL	Consider the other pointer.
		LD	DE,+168F	Use line number zero.

The usual entry point is at LINE-NO.

1695	LINE-NO	LD	A,(HL)	Fetch the high byte and
		AND	+C0	test it.
		JR	NZ,1691,LINE-NO-A	Jump back if not suitable.
		LD	D,(HL)	Fetch the high byte.
		INC	HL
		LD	E,(HL)	Fetch the low byte and
		RET		return.

THE 'RESERVE' SUBROUTINE
This subroutine is normally called by using RST 0030,BC-SPACES.
On entry here the last value on the machine stack is WORKSP and the value above it is the number of spaces that is to be 'reserved'.
This subroutine always makes 'room' between the existing work space and the calculator stack.

169E	RESERVE	LD	HL,(STKBOT)	Fetch the current value of
		DEC	HL	STKBOT and decrement it to
				get the last location of the
				work space.
		CALL	1655,MAKE-ROOM	Now make 'BC spaces'.
		INC	HL	Point to the first new space
		INC	HL	and then the second.
		POP	BC	Fetch the old value of
		LD	(WORKSP),BC	WORKSP and restore it.
		POP	BC	Restore BC - number of spaces.
		EX	DE,HL	Switch the pointers,
		INC	HL	Make HL point to the first of
				the displaced bytes.
		RET		Now return.

Note: It can also be considered that the subroutine returns with the DE register pair pointing to a 'first extra byte' and the HL register pair pointing to a 'last extra byte', these extra bytes having been added after the original '(HL)+1' location.

THE 'SET-MIN' SUBROUTINE
This subroutine resets the editing area and the areas after it to their minimum sizes.  In effect it 'clears' the areas.

16B0	SET-MIN	LD	HL,(E-LINE)	Fetch E-LINE.
		LD	(HL),+0D	Make the editing area hold
		LD	(K-CUR),HL	only the 'carriage return'
		INC	HL	character and the end marker.
		LD	(HL),+80
		INC	HL	Move on to clear the work
		LD	(WORKSP),HL	space.

Entering here will 'clear' the work space and the calculator stack.

16BF	SET-WORK	LD	HL,(WORKSP)	Fetch the WORKSP.
		LD	(STKBOT),HL	This clears the work space.