_get_degree:
; input: hl = ptr to binary polynomial (little endian-encoded)
; degree in a
; destroys: bc, flags
	ld bc, 29
	add hl, bc
	ld c, 30
.byte_loop:
	ld a, (hl)
	or a			; if byte is 0
	jr nz, .found_byte
	ld a, d
	sub a, 8
	ld d, a
	dec hl
	dec c
	jr nz .byte_loop
; exit
	ld a, -1
	ret

.found_byte:
; process bits
	ld b, 8
.bit_loop:
	rla
	jr c, .found_bit
	dec d
	djnz .bit_loop

.found_bit:
	ld a, c
	dec a
	dec b
	add a, a
	add a, a
	add a, a
	or a, b
	ret