title	Module from library C_1 : SBRK
	name	('SBRK')

; Allocate memory

; ENTRY	Reg HL holds bytes to be requested

; EXIT	Reg HL holds pointer to cntiguous block of memory
;	If not enough memory available, reg HL returns 0

; NOTE	Routine assumes stack growing down from top of memory
;	Location at SBRK-2 holds number of bytes to be reserved
;	for the stack - it defaults to 1024

; Copyright (C)	Werner Cirsovius
;		Hohe Weide 44
;		D-20253 Hamburg
;		Tel.:040/4223247

;		Version 1.0, July 1994

BDOS	equ	0005h

	entry	sbrk

	extrn	$memry

	dw	1024
sbrk:
	ex	de,hl
	push	bc
	ld	hl,(BDOS+1)	; Get top of memory
	ld	bc,(sbrk-2)	; .. fetch stack reserve
	or	a
	sbc	hl,bc		; .. calculate max top
	ld	b,h
	ld	c,l
	ld	hl,($memry)	; Get current top of heap
	ex	de,hl
	add	hl,de		; .. calculate new top
	push	hl
	or	a
	sbc	hl,bc		; Test enough memory
	pop	hl
	pop	bc
	jr	c,got.mem
	ld	hl,0		; Return no space
	ret
got.mem:
	ld	($memry),hl	; Save new heap
	ex	de,hl		; .. get back start
	ret

	end