RR	D	Rotate right with carry D', E',
		RR	E	D & E.
		EXX		Thereby shifting the whole five
		RR	D	bytes of the number to the right
		RR	E	as many times as B counts.
		DJNZ	2FE5,ONE-SHIFT	Loop back until B reaches zero.
		POP	BC	Restore the original BC.
		RET	NC	Done if no carry to retrieve.
		CALL	3004,ADD-BACK	Retrieve carry.
		RET	NZ	Return unless the carry rippled
				right back. (In this case there is
				nothing to add).
2FF9	ADDEND-0	EXX		Fetch L', D' & E'.
		XOR	A	Clear the A register.
2FFB	ZEROS-4/5	LD	L,+00	Set the addend to zero in D',E',
		LD	D,A	D & E, together with its marker
		LD	E,L	byte (sign indicator) L', which
		EXX		was Hex.00 for a positive
		LD	DE,+0000	number and Hex.FF for a
				negative number. ZEROS-4/5
				produces only 4 zero bytes
				when called for near underflow
				at 3160.
		RET		Finished.

THE 'ADD-BACK' SUBROUTINE
This subroutine adds back into the number any carry which has overflowed to the right. In the extreme case, the carry ripples right back to the left of the number.
When this subroutine is called during addition, this ripple means that a mantissa of 0.5 was shifted a full 32 places right, and the addend will now be set to zero; when called from MULTIPLICATION, it means that the exponent must be incremented, and this may result in overflow.

3004	ADD-BACK	INC	E	Add carry to rightmost byte.
		RET	NZ	Return if no overflow to left.
		INC	D	Continue to the next byte.
		RET	NZ	Return if no overflow to left.
		EXX		Get the next byte.
		INC	E	Increment it too.
		JR	NZ,300D,ALL-ADDED	Jump if no overflow.
		INC	D	Increment the last byte.
300D	ALL-ADDED	EXX		Restore the original
				registers.
		RET		Finished.

THE 'SUBTRACTION' OPERATION
(Offset 03 - see CALCULATE below: 'subtract')

This subroutine simply changes the sign of the subtrahend and carried on into ADDITION.
Note that HL points to the minuend and DE points to the subtrahend. (See ADDITION for more details.)

300F	SUBTRACT	EX	DE,HL	Exchange the pointers.
		CALL	346E,NEGATE	Change the sign of the
				subtrahend.
		EX	DE,HL	Exchange the pointers back and
				continue into ADDITION.

THE 'ADDITION' OPERATION
(Offset 0F - see CALCULATE below: 'addition')

The first of three major arithmetical subroutines, this subroutine carries out the floating-point addition of two numbers, each with a 4-byte mantissa and a 1-byte exponent. In these three subroutines, the two numbers at the top of the calculator stack are added/multiplied/divided to give one number at the top of the calculator stack, a 'last value'.