title	Module from library BASE_1 : DECRRN
	name	('DECRRN')
	maclib	baselib.lib

; Decrement random record number - 24 bit value

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

;		Version 1.0 September 1991

; ENTRY	Accu and reg pair HL hold value
;	Accu holds high byte

; EXIT	Accu and reg pair HL hold value decremented by one

	entry	decrrn

decrrn:
	push	bc
	ld	b,a
	or	l		; Ignore zero
	or	h
	ld	a,b
	pop	bc
	ret	z
	bit	7,h		; Mark sign of middle byte
	dec	hl		; Decrement low and middle
	ret	nz		; .. end on ole bit set
	bit	7,h		; Test carry
	ret	z		; .. nope
	dec	a		; Bump
	ret

	end