.TITLE	IVIRT
;
; ROUTINE TO ALLOW A FORTRAN PROGRAM TO PASS A VIRTUAL ADDRESS AS AN
; ARGUMENT TO A SUBROUTINE.  IT WAS DESIGNED TO BE USED IN CONJUNCTION
; WITH PLAS (ALLOWS PLAS MAPPING VALUES TO BE PASSED AS A ARRAY).
; IN THE EXAMPLE
;
;	CALL SUB(IVIRT("40000))
;
; THE SUBROUTINE SUB WILL USE THE CONTENTS OF VIRTUAL ADDRESS 40000 OCTAL
; AS THE LOCATION OF THE IT'S ARGUMENT.
;
; NOTE: THIS ROUTINE WILL WORK WITH FORTRAN 4-PLUS ONLY AS WILL ALTER THE
;	CODE GENERATED FOR SUBROUTINE LINKAGE.
;
; WRITTEN  NOVEMBER 1977   R B FRENCH     THE BOEING COMPANY
;
IVIRT::	MOV	(SP),R0		;GET RETURN ADDRESS
	CMP	2(R0),#10667	;IS IT  MOV  SP,LIST ?
	BEQ	10$		;BRANCH IF SO
	CMP	2(R0),#10067	;ALREADY CHANGED TO  MOV  R0,LIST  ?
	BEQ	RET		;THEN JUST RETURN
	MOV	#-1,R0		;SOMETHINGS WRONG - MAKE ARGUMENT NULL
	BR	RET		;AND JUST RETURN
10$:	MOV	#10067,2(R0)	;CHANGE TO  MOV  R0,LIST
	MOV	@2(R5),R0	;AND SET VIRTUAL ADDRESS IN R0
RET:	RTS	PC
	.END