; out	ds:si	copy of interrupt table
ivt_backup:
  push ax
  push cx
  push di ; backup original value
  push ds
  mov ax, 0x80
  call malloc
  push di
  mov cx, 0x80
  mov ax, cs
  mov es, ax
  mov si, 0x0000
  mov ds, si
  rep movsb
  pop si ; this was di after malloc
  pop ds
  pop di ; restore original di
  pop cx
  pop ax
  ret

; set item in interrupt vector table
; in:	bx	interrupt number
;	ds:dx	new handler address
ivt_set:
  push es
  push ax

  xor ax,ax
  mov es,ax

  sal bx,1
  sal bx,1

  mov [es:bx], dx
  mov [es:bx+2], ds

  pop ax
  pop es
  ret