; Get pointer to interrupt vector
	; IN	al	number
	; OUT	0:bx	ptr to vector
intr_ptr:
	xor bh, bh
	mov bl, al
	add bx, bx
	add bx, bx
	ret

	; Set interrupt vector
	; IN	al	number
	;	ds:dx	ptr
intr_set:
	push bx
	call intr_ptr
	ss mov [bx], dx
	ss mov [bx+2], ds
	pop bx
	ret

	; Get interrupt vector
	; IN	al	number
	; OUT	es:bx	ptr
intr_get:
	call intr_ptr
	ss mov es, [bx+2]
	ss mov bx, [bx]
	ret

	; Save BIOS vectors
	; Trashes ax, cx, bx, ds
intr_backup:
	mov cx, 0x20
	xor bx, bx
	mov ds, bx
.loop:	; load segment
	mov ax, [bx+2]
	; skip transfer if not pointing to BIOS
	cmp ax, 0xA000
	jc .skip
	; store segment
	mov [bx+ivt2+2], ax
	; copy offset
	mov ax, [bx]
	mov [bx+ivt2], ax
	; iterate to next vector
.skip:	add bx, 4
	loop .loop
	ret

	; Restore BIOS vectors
intr_restore:
	mov cx, 0x20
	xor bx, bx
	mov ds, bx
.loop:	; load segment
	mov ax, [bx+ivt2+2]
	; skip if not a vector to BIOS
	cmp ax, 0xA000
	jc .skip
	; store segment
	mov [bx+2], ax
	; copy offset
	mov ax, [bx+ivt2]
	mov [bx], ax
	; iterate to next vector
.skip:	add bx, 4
	loop .loop
	ret