assembly4

	.include "m168def.inc"
							; start defines
	.def counter = R16		; number of array values
	.def first_v = R17		; first value
	.def second_v = R18		; second value
	.def temp = R19			; temporary value
	.def suit_num = R20		; suitable numbers
							; end defines

	.dseg					; start segment of data
	.org SRAM_START
	table: .byte 10
							; end segment of data

	.cseg					; start segment of code
	;array: .db 2, 4, 8, 12, 8, 10, 12, 14, 16, 18
	array: .db 2, 0, 4, 8, 12, 2, 0, 2, 18, 16
	ldi ZH, high(array)		; pointer to array
	ldi ZL, low(array)
	ldi XH, high(table+1)	; pointer to second value
	ldi XL, low(table+1)	; in table

	ldi counter, 10			; number of value to check
	ldi suit_num, 0			; number of suitable numbers
start:
	lpm first_v, Z+
	lpm second_v, Z
	dec counter				; decrease value to check
	breq final				; end loop if counter == 0 

							/* if
							??????1? (...0?) - number 1
							??????0? (...1?) - number 2
							conclusion: numbers differ by 2 */

	andi first_v, 0b10		; logical AND with 2
	mov temp, second_v
	andi temp, 0b10			; logical AND with 2
	cp first_v, temp
	brne modulo_by_4		; if numbers have different second bits
							; then check his modulo (see above why)
	rjmp start				; repeat loop

modulo_by_4:
							; 00000000 - 8 bit
							; ??????00 - number multiplicity by 4
	sbrc second_v, 0		; skip next cmd IF first bit == 0
	rjmp start				; otherwise goto main loop
	sbrc second_v, 1		; skip next cmd IF second bit == 0
	rjmp start				; otherwise goto main loop

							; add it number to table:
	inc suit_num			; increase number of suitable numbers
	st X+, second_v			; current number to X
	rjmp start				; goto main loop
final:
	sts table, suit_num		; write number of suitable number to
							; first byte of table
end:						; endless loop
	rjmp end