.TITLE	JSUB
	.IDENT	/V1.01/
	.PSECT	CODE,RO
	.NLIST	SYM,TOC
 
; DOUBLE-PRECISION INTEGER SUBTRACTION
;
; 'PROCEDURE' JSUB(JDIFF,JA,JB);
;
; JDIFF:=JA-JB
 
G1572::	CMP	(%2)+,(%3)+	; ADDRESS LO WORDS
	MOV	(%2),%4		; GET JA LOW
	SUB	(%3),%4		; SUB JB LO
	MOV	-(%2),%5	; GET JA HI, W/O AFFECTING CARRY
	SBC	%5		; INCLUDE BORROW
	BVS	10$		; TRAP OVERFLOW
	SUB	-(%3),%5	; ELSE SUBTRACT JB HI
	BVC	100$		; EXIT IF OK
	BR	11$		; BUT TRAP OVERFLOW AGAIN
 
10$:	SUB	-(%3),%5	; COMPLETE SUM IF OVERFLOW ON SBC
11$:	DEC	V		; DEC OVERFLOW COUNTER
	MOV	#786.,FLOERR	; SET UP FLOERRORCODE
 
100$:	MOV	%5,(%1)+	; STORE RESULT HI
	MOV	%4,@%1		; AND LO
	ADD	#2,@SP		; STANDARD EXIT
	RTS	PC
 
	.PSECT	GLOBAL,OVR,GBL,RW
 
G=.
 
V=G+300.
FLOERR=G+302.
 
	.END