6500/libem/gto.s

.define Gto
.sect .text
.sect .rom
.sect .data
.sect .bss
.sect .text

! This subroutine performs the non_local goto.
! The address of the descriptor is stored in zeropage locations
! ADDR, ADDR+1.
! Since there are two stacks (hardware_stack and the real_stack),
! the stackpointer of the hard_stack is resetted by searching the
! new localbase in the real_stack while adjusting the hardware_stack.


Gto:
        stx ADDR        ! address of descripto (lowbyte)
        sta ADDR+1      ! address of descriptor (highbyte)
        pla             ! remove
        pla             ! __gto return address.
        ldy #4
        lda (ADDR),y    ! new localbase (lowbyte)
        sta ARTH
        tax
        iny
        lda (ADDR),y    ! new localbase (highbyte)
        sta ARTH+1
        cmp LB+1
        bne 1f
        cpx LB
        beq 2f          ! goto within same procedure
    1:  ldy #0
        lda (LB),y      ! get localbase (lowbyte)
        tax
        iny
        lda (LB),y      ! get localbase (highbyte)
        cmp ARTH+1
        bne 3f
        cpx ARTH
        beq 2f          ! found localbase
    3:  stx LB          ! temporary save of localbase
        sta LB+1
        pla             ! adjust
        pla             ! hardware_stack
        jmp 1b
    2:  sta LB+1        ! store localbase (highbyte)
        pha
        stx LB          ! store localbase (lowbyte)
        sec
        txa
        sbc #BASE
        sta LBl         ! localbase - 240 (lowbyte)
        pla
        sbc #0
        sta LBl+1       ! localbase - 240 (highbyte)
        ldy #3
        lda (ADDR),y    ! new stackpointer (highbyte)
        sta SP+1
        dey
        lda (ADDR),y    ! new stackpointer (lowbyte)
        sta SP+2
        dey
        lda (ADDR),y    ! jump address (highbyte)
        sta ADDR+3
        dey
        lda (ADDR),y    ! jump address (lowbyte)
        sta ADDR+2
        jmp (ADDR+2)    ! jump to address


1	.define Gto
2	.sect .text
3	.sect .rom
4	.sect .data
5	.sect .bss
6	.sect .text
7
8	! This subroutine performs the non_local goto.
9	! The address of the descriptor is stored in zeropage locations
10	! ADDR, ADDR+1.
11	! Since there are two stacks (hardware_stack and the real_stack),
12	! the stackpointer of the hard_stack is resetted by searching the
13	! new localbase in the real_stack while adjusting the hardware_stack.
14
15
16	Gto:
17	stx ADDR ! address of descripto (lowbyte)
18	sta ADDR+1 ! address of descriptor (highbyte)
19	pla ! remove
20	pla ! __gto return address.
21	ldy #4
22	lda (ADDR),y ! new localbase (lowbyte)
23	sta ARTH
24	tax
25	iny
26	lda (ADDR),y ! new localbase (highbyte)
27	sta ARTH+1
28	cmp LB+1
29	bne 1f
30	cpx LB
31	beq 2f ! goto within same procedure
32	1: ldy #0
33	lda (LB),y ! get localbase (lowbyte)
34	tax
35	iny
36	lda (LB),y ! get localbase (highbyte)
37	cmp ARTH+1
38	bne 3f
39	cpx ARTH
40	beq 2f ! found localbase
41	3: stx LB ! temporary save of localbase
42	sta LB+1
43	pla ! adjust
44	pla ! hardware_stack
45	jmp 1b
46	2: sta LB+1 ! store localbase (highbyte)
47	pha
48	stx LB ! store localbase (lowbyte)
49	sec
50	txa
51	sbc #BASE
52	sta LBl ! localbase - 240 (lowbyte)
53	pla
54	sbc #0
55	sta LBl+1 ! localbase - 240 (highbyte)
56	ldy #3
57	lda (ADDR),y ! new stackpointer (highbyte)
58	sta SP+1
59	dey
60	lda (ADDR),y ! new stackpointer (lowbyte)
61	sta SP+2
62	dey
63	lda (ADDR),y ! jump address (highbyte)
64	sta ADDR+3
65	dey
66	lda (ADDR),y ! jump address (lowbyte)
67	sta ADDR+2
68	jmp (ADDR+2) ! jump to address
69
70