.TITLE	VIRABS - ROUTINE TO CONVERT VIRT # TO ABS INTEGER

.IDENT	'VITA00'

.PSECT	VIRABS

;	KEN DEMERS
;	UTRC
;	NOVEMBER 1979

;	THIS ROUTINE CONVERTS A F.P. VIRTUAL NUMBER
;	TO A ABSOLUTE INTEGER SCREEN COORDINATE. THE
;	CONVERSION IS DONE USING THE COORDINATE SYSTEM
;	(WINDOW) ESTABLISHED BY GRID

;	EDIT HISTORY

;	5-MAY-80	++01	RESULT IS ROUNDED


;	ON ENTRY:

;	AC0	= F.P. OF ABSOLUTE INTEGER MAX
;	AC1	= F.P. OF MAX RANGE
;	R0	= A(VIRTUAL F.P. # TO BE CONVERTED)

;	INTERNAL GLOBALS

.GLOBL	V$IRABS


;	ASSIGNMENTS

AC0	= %0			;FPP ACCUMULATOR 0
AC1	= %1
AC2	= %2
AC3	= %3
AC4	= %4



V$IRABS: CALL	S$AVARG		;SAVE REGS
	STF	AC0,AC3		;SAVE AC0
	STF	AC1,AC4		;SAVE AC1
	MULF	(R0),AC3	;VIRT # * MAX OF AXIS
	TSTF	AC4		;TST RANGE
	CFCC			;GET COND CODES
	BGE	VIR10		;RANGE WAS POS
	NEGF	AC4		;MAKE IT POS
VIR10:	DIVF	AC4,AC3		;GET ABS #
	ADDF	HALF,AC3	;++01 ROUND THE # UP
	CALL	R$STARG		;RESTORE REGS
	STCFI	AC3,R0		;ON EXIT R0= INT OF RESULT
	RETURN

HALF:	.FLT2	.5		;CONSTANT USED TO ROUND UP
	.END