; Contains code licensed under CC-BY-SA by Michael Karcher
;  from https://retrocomputing.stackexchange.com/questions/12693/how-does-single-stepping-on-the-8086-interact-with-internal-and-external-interru/12694#12694
;  2026 by E. C. Masloch

	cpu 8086
	org 256
start:
	cmp sp, stack.top
	jb error
	mov si, 81h
	call getnumber
	mov word [counter], di
	dec si
scan:
.:	lodsb
	cmp al, 32
	je .
	cmp al, 9
	je .
	cmp al, 13
	je .end
	cmp al, '!'
	jne .notex
	mov word [..@multiply], 9090h
	jmp .

.notex:
	cmp al, '?'
	jne .notq
	call getnumber
	mov word [..@counter], di
	dec si
	jmp .

.notq:
	cmp al, '+'
	jne .notplus
	inc byte [..@list]
	jmp .

.notplus:
	jmp error

.end:

hook:
	mov ax, 3501h
	int 21h
	mov word [i01.next], bx
	mov word [i01.next + 2], es
	mov dx, i01
	mov ax, 2501h
	int 21h

	mov ax, 35A1h
	int 21h
	mov word [iA1.next], bx
	mov word [iA1.next + 2], es
	mov dx, iA1
	mov ax, 25A1h
	int 21h

%define STRINGS db ""
%define TABLE dw ""

%imacro i 1+.nolist
 %assign %%entry ($ - start + 256)
 %defstr %%string %1
 %xdefine STRINGS STRINGS, %%name:, {db %%string, 36}
 %xdefine TABLE TABLE, dw %%entry, dw %%length, dw %%name
	%1
 %assign %%length ($ - start + 256) - %%entry
%endmacro

	align 64, nop
test:
; Following from https://retrocomputing.stackexchange.com/questions/12693/how-does-single-stepping-on-the-8086-interact-with-internal-and-external-interru/12694#12694
i pushf
i mov  ax, 300h      ; 100h = TF; 200h = IF
i push ax
i popf               ; This instruction sets the trace flag
i mov  ax, 1234h
i mov  bl, 1    
i inc  ax       
i mov  dx, ds   
i mov  es, ax        ; On 8086/8088: No interrupts before NOP is executed
i nop           
i mov  dx, ss   
i mov  ss, dx        ; On any x86 processor: No interrupts before NOP is executed
i nop           
i int  0A1h     
i dec  cx       
i popf               ; This instruction clears the trace flag
i dec  ax

unhook:
	lds dx, [cs:i01.next]
	mov ax, 2501h
	int 21h

	lds dx, [cs:iA1.next]
	mov ax, 25A1h
	int 21h

dump:
	 push cs
	 pop ds
	 push cs
	 pop es
	mov si, buffer
	mov di, [next]
	mov ax, di
	sub ax, si
	shr ax, 1
	shr ax, 1
	call disp_ax_hex

	mov dx, msg.linebreak
	call disp_msg

	mov bx, cs
	xchg cx, ax
	int3
	cmp byte [..@list], 1
	jb dumponly
list:
	push si
	push cx
	mov si, table
.loop:
	lodsw

	mov dx, msg.asterisk
	mov di, buffer
	push cx
.next:
	scasw
	je .found
	scasw		; di += 2
	loop .next
.notfound:
	mov dx, msg.blank
.found:
	call disp_msg
	pop cx
	call disp_ax_hex
	mov dx, msg.plus
	call disp_msg
	lodsw
	call disp_al_dec
	mov dx, msg.sep
	call disp_msg
	lodsw
	xchg dx, ax
	call disp_msg
	mov dx, msg.linebreak
	call disp_msg

	cmp si, table.end
	jb .loop
.end:
	pop cx
	pop si
	cmp byte [..@list], 2
	jb exit
dumponly:
	jcxz .done
.loop:
	lodsw
	xchg ax, dx
	lodsw
	call disp_ax_hex
	call disp_colon
	xchg ax, dx
	call disp_ax_hex
	cmp dx, bx
	je .ourcs
	mov dx, msg.not_our_cs
	call disp_msg
	jmp .next

.ourcs:
	mov di, table
.innerloop:
	scasw
	jne .innernext
	add ax, word [di + 0]
	mov dx, msg.sep
	call disp_msg
	call disp_ax_hex
	mov dx, msg.sep
	call disp_msg
	mov dx, word [di + 2]
	call disp_msg
	mov dx, msg.linebreak
	call disp_msg
	jmp .next

.innernext:
	scasw			; di += 2
	scasw			; di += 2
	cmp di, table.end
	jb .innerloop
	mov dx, msg.unknownline
	call disp_msg
.next:
	loop .loop
.done:

exit:
	mov ax, 4C00h
	int 21h

error:
    mov dx, msg.error
    call disp_msg
    mov ax, 4C01h
    int 21h

disp_msg:
	push ax
	mov ah, 09h
	int 21h
	pop ax
	retn

disp_colon:
	push ax
	push dx
	mov dl, ':'
	mov ah, 02h
	int 21h
	pop dx
	pop ax
	retn

retf_inst:
	retf

	align 2
iA1:
i	jmp strict short .enter
.next:	dd 0
	dw "KB"
	db 0
	jmp strict short retf_inst
	times 7 db 0
.enter:
i	inc dx
i	dec dx
i	iret

	align 2
i01:
	jmp strict short .enter
.next:	dd 0
	dw "KB"
	db 0
	jmp strict short retf_inst
	times 7 db 0
.enter:
	push bp
	mov bp, sp
	push es
	push di
	push ax
	push cx
	push dx
	cld
	 push cs
	 pop es
	mov di, [es:next]
	cmp di, buffer.end
	jb .space
	inc word [es:toomany]
	jmp .done

.space:
	mov ax, word [bp + 2]	; ip
	stosw
	mov ax, word [bp + 4]	; cs
	stosw
	mov word [es:next], di
.done:

    mov cx, word [es:counter]
    jcxz .skip
    cli
.outer:
    push cx
    mov cx, -1
..@counter: equ $ - 2
.inner:
    mov ax, 16661
..@multiply:
    mul ax
    add ax, ax
    loop .inner
    pop cx
    loop .outer
.skip:
	pop dx
	pop cx
	pop ax
	pop di
	pop es
	pop bp
	iret

disp_ax_hex:
    xchg al, ah
    call disp_al_hex
    xchg al, ah
disp_al_hex:
    push cx
    mov cl, 4
    rol al, cl
    call disp_al_nybble_hex
    rol al, cl
    pop cx
disp_al_nybble_hex:
    push ax
    push dx
    and al, 15
    add al, '0'
    cmp al, '9'
    jbe .got
    add al, 7
.got:
    xchg dx, ax
    mov ah, 02h
    int 21h
    pop dx
    pop ax
    retn


disp_al_dec:
	push ax
	push cx
	push dx
	mov cx, 100 << 8; ch = 100, cl = 0
.loop:
	mov ah, 0	; ax = dividend
	div ch		; ah = remainder, al = quotient
	 push ax
	test al, al	; leading zero ?
	jnz .do		; no -->
	test cx, 01FFh	; (ch & 1) == 0 (not true for 100, 10)
			;  AND cl == 0
	jz .dont	; then skip leading zero -->
.do:
	inc cx		; remember had a digit
	add al, '0'
	xchg dx, ax
	mov ah, 02h
	int 21h
.dont:
	mov al, ch
	aam		; divide by 10
	mov ch, ah
	 pop ax
	mov al, ah
	cmp ch, 1
	jae .loop
	pop dx
	pop cx
	pop ax
	retn


		; INP:	si -> text
		; OUT:	si - 1 -> end (nondigit)
		;	di = number
getnumber:
.skip:
    lodsb
    cmp al, 32
    je .skip
    cmp al, 9
    je .skip
    cmp al, '0'
    jb error
    cmp al, '9'
    ja error
    xor di, di
    jmp .digit
.loop:
    lodsb
.digit:
	cmp al, '_'
	je .loop
    sub al, '0'
    jb .end
    cmp al, 10
    jae .end
    cbw
    add di, di  ; times 2
    mov bx, di
    add di, di  ; times 4
    add di, di  ; times 8
    add di, bx  ; times 10
    add di, ax
    jmp .loop

.end:
	retn

%imacro dumptables 1-*.nolist
 %rep %0
	%1
  %rotate 1
 %endrep
%endmacro

	align 2, db 0
table:
dumptables TABLE
.end:

next:	dw buffer
toomany:dw 0
..@list:db 0

msg:
.sep:		db "  ",36
.linebreak:	db 13,10,36
.not_our_cs:	db "  Not in our CS",13,10,36
.unknownline:	db "  Unknown line in our CS",13,10,36
.error:		db "Error!",13,10,36
.asterisk:	db "*",36
.blank:		db " ",36
.plus:		db "+",36
dumptables STRINGS

	absolute $

	alignb 2
counter:resw 1

	alignb 4
buffer:
	resd 512
.end:

	alignb 16
stack:
	resb 512
.top: