title	Module from library BASE_2 : CHNUSR
	name	('CHNUSR')
	maclib	baselib.lib

; Perform disk I/O for different user areas

; Copyright (C)	Werner Cirsovius
;		Hohe Weide 44
;		D-20253 Hamburg
;		Tel.: +49-40-4223247

;		Version 1.0 February 1987

; ENTRY	Reg pair BC holds disk function to be performed
;	Reg pair DE holds FCB
;	Reg pair HL points to user location -1

; EXIT	Carry set indicates disk error

	entry	@chusr

	extrn	usrget,usrset

@chusr:
	push	hl
	push	bc
	pop	hl
	ld	(usr+1),hl	; Set vector
	pop	hl
	inc	hl		; Fix user location
	ld	a,(hl)		; Get user
	inc	a		; Test requested
	jr	z,usr
	call	usrget
	ld	(curus),a	; Save current user
	ld	a,(hl)
	call	usrset		; Set new one
usr:
	call	$-$		; Put vector
	push	af		; Save resulting code
	ld	a,(hl)		; Test user to restore
	inc	a
	jr	z,nousr
	ld	a,(curus)
	call	usrset		; Restore
nousr:
	dec	hl		; Fix pointer
	pop	af		; Get disk code
	ret

	dseg

curus:
	ds	1		; Hold current user

	end