ALWAYS	31JAN4	REVERSE	<REVERSE - REVERSE RANGE OF VIRTUAL MEMORY>
	.MCALL	DIR$,CALLR
;************************************************************************
;*									*
;*	MODULE:	REVERSE - REVERSE A SPECIFIED RANGE OF VIRTUAL MEMORY	*
;*							IN PLACE	*
;*									*
;*	AUTHOR: Chris Doran, Sira Ltd					*
;*									*
;*	DATE:	31-JAN-84						*
;*									*
;*	INPUT PARAMETERS:						*
;*									*
;*		R0 POINTS TO THE COMMAND LINE IN PROCESS		*
;*									*
;*	OUTPUT PARAMETERS:						*
;*									*
;*		R0 POINTS JUST BEYOND THE LAST CHARACTER OF THE COPY	*
;*									*
;*	DESTROYS: R1,R2,R3,R4,R5					*
;*									*
;************************************************************************

REVERSE::
	CALL	FROMTH		; Collect FROM/THRU/STEP/COUNT arguments
	BCS	250$		;  CS: FAILED
	ROR	%3		; Halve count w/o sign extend (cc from FROMTH)
	BEQ	250$		; Nothing to do if count was 1
	ADD	#MEMORY,%1	; Set pointers to real addresses: bottom (FROM)
	ADD	#MEMORY,%2	;  and top (THRU)

; Swap %3=COUNT/2 bytes, decrementing top pointer and incrementing bottom.
10$:
	MOVB	@R1,%4		; Get byte from bottom address
	MOVB	@%2,@%1		; Copy in byte from top
	MOVB	%4,@%2		; Complete exchange
	ADD	STEP,%1		; Increment bottom location
	SUB	STEP,%2		; Decrement top location
	SOB	%3,10$		; Let's do it again
250$:
	CLC			; Normal exit = success
	
255$:				; ERROR EXIT
	CALLR	EXTRA		; PURGE EXTRA & RETURN

	.END