title	start up code for assembly langauge
	include	asm.inc

	dosseg
NULL	segment	para public 'BEGDATA'
NULL	ends

	public	psp,startup,dgroup_segment,top_of_stack,initterm,xcbegin,xcend


XIB	segment word public 'DATA'	; these segments contain a list of
xibegin	label	word			;  procedure addresses that the
XIB	ends				;  start-up code calls before main
XI	segment word public 'DATA'
XI	ends
XIE	segment word public 'DATA'
xiend	label	word
XIE	ends

XPB	segment word public 'DATA'	; these segments contain a list of
xpbegin	label	word			;  procedure addresses that the
XPB	ends				;  start-up code calls before
XP	segment word public 'DATA'	;  returning control to ms-dos.  they
XP	ends				;  are called only on a full exit.
XPE	segment word public 'DATA'	;  
xpend	label	word
XPE	ends

XCB	segment word public 'DATA'	; these segments contain a list of
xcbegin	label	word			;  procedure addresses that the
XCB	ends				;  start-up code calls before
XC	segment word public 'DATA'	;  returning control to ms-dos.  they
XC	ends				;  are ALWAYS called regardless of how
XCE	segment word public 'DATA'	;  the program terminates.
xcend	label	word
XCE	ends

DGROUP	group	XIB,XI,XIE,XPB,XP,XPE,XCB,XC,XCE

	.data
psp			dw	0
dgroup_segment		dw	0


	.data?
	extb	_edata,_end

top_of_stack		dw	?


	.code
	extn	set_argc_argv,ms_dos,main,exit_program


;;	initterm
;
;	entry	SI	initializer or terminator list
;		DI	end of list
;	may use	AX,BX,CX,DX,DI,SI,DS,ES
;
initterm proc
	movx	ds,DGROUP_SEGMENT	; call list of initializers or
iit1:	cmp	si,di			;  terminators
	jae	iit2			;   if end of list
	lodsw
	or	ax,ax
	jz	iit1			;   if NULL address

	pushm	di,si,ds
	call	ax
	popm	ds,si,di
	jmp	iit1
iit2:	ret
initterm endp


;;	startup
;
;	entry	AX	offset stack
;		ES	program segment prefix
;		SS	DGROUP
;	exit	BP	0
;	may use	AX,BX,CX,DX,DI,SI,DS,ES
;
startup proc
	cld
	movx	bp,0			; BP=0 in TIGHT model

	mov	ax,ss			; compensate for Microsoft LINK bug
	mov	dx,DGROUP		;  where SS is wrong segment
	sub	ax,dx
	jbe	sta1			;  if SS is DGROUP, must be OPTLINK
	mov	cl,4			;  else MS-LINK, fix stack pointer
	shl	ax,cl
	mov	ss,dx
	add	sp,ax

sta1:	mov	top_of_stack[bp],sp
	mov	psp[bp],es

	mov	ax,sp			; compute number of paragraphs
	add	ax,15			;  in program
	mov	cl,4
	shr	ax,cl
	mov	bx,ss
	add	bx,ax
	sub	bx,psp[bp]

	mov	ah,4Ah			; shrink program memory block for
	call	ms_dos			;  dynamic storage system

	mov	dgroup_segment[bp],ss

	mov	al,0			; zero BSS segment
	mov	cx,offset DGROUP:_end
	movx	es,DGROUP_SEGMENT
	mov	di,offset DGROUP:_edata
	sub	cx,di
	rep	stosb

	call	set_argc_argv		; process command line

	lea	di,xiend		; call initializers
	lea	si,xibegin
	call	initterm

	movx	ds,DGROUP_SEGMENT	; call user's program
	movx	es,DGROUP_SEGMENT
	call	main

	lea	di,xpend		; call on-exit routines
	lea	si,xpbegin		;  (must call on-exits before
	call	initterm		;   terminators!)

	lea	di,xcend		; call terminators
	lea	si,xcbegin
	call	initterm

	jmp	exit_program
startup endp

	end	startup