Fibonaci sequence for the DCPU-16

gistfile1.dasm16

;This program writes the first 24 terms of the Fibonacci sequence(after that it overflows anyways) to the
;display of the DCPU-16 from 0x10c.
;It is my first ever assembly program, so it is probably quite horribly, but there isn't that many examples
;floating around, so i thought this might be useful.
;this works in the dcpu-emu program by interfect(https://bitbucket.org/interfect/dcpu-emu/overview) it might
;work elsewhere too, but it think that one is the only one which has the display implemented.
;Last note: I wrote all the comments in like 5 minutes, so they are not that good, and there might be
;grammatical/spelling/other mistakes.


	set B, 0			;the 0th fib term, does not get printed
	set A, 1			;the 1th fib term, get printed 
:ol	ife J, 24			;loop 24 times
		set PC, end		;jump to end when done
	jsr asc				;compute the 4 ASCII chars for the value in A (the current fib term)
	set X, 5					
	mul X, J			;X is the offset from where we want to draw ASCII chars
	set I, 0			;initialize I to 0
:l	ife I, 4			;There are 4 ASCII chars, loop through them
		set PC, el		;Jump to el when done
	set [0x8000+X], [data+I]	;Write the Ith charater to the offset defined by X
	add X, 1			;increment X
	add I, 1			;increment I
	set PC, l			;loop

:el	set C, A			;Here the fib computation takes place. C is a temp val for A
	add A, B			;The next fib term is given by adding the two previous
	set B, C			;Set the current term, to the last.
	add J, 1			;increment J
	set PC, ol			;loop
:end	sub PC, 1			;Halt the program by looping forever.


;asc is a procedure that reads the number in register A and computes the ASCII code
;for each digit of the number. The ascii codes is stored in the "array" data, which
;is 4 words long.

:asc	set PUSH, A
	set PUSH, B
	set PUSH, C
	set PUSH, X
	set PUSH, Y
	set PUSH, I			;Pushing stuff to stack, so we can use the registers.

	set I, 0
:loop	ife I, 4			;There are 4 digits, loop through them
		set PC, done		;go to done when done
	set C, data			;let C point to the data, not sure if neccesary
	add C, I			;let C point to digit number I

	set [C], A			;Put A into the data array, now we will isolate the
						;Ith digit.
	set B, 0xf000			;B is the mask we will use to iso late a single HEX digit
	set X, 4
	mul X, I			;X is the amount to right shift the mask
	set Y, 12
	sub Y, X			;Y is the amount to right shift the number afterwards
					;X+Y = 12, so the digit will always use the first 4 bits
	shr B, X			;Shift the mask to get the Ith digit

	and [C], B			;apply the mask
	shr [C], Y			;shift the value so it occupies the first 4 bits/nibble

	ifg [C], 0x9			;check if the value is 0-9 or A-F
		set PC, lett		;the printed char should be a letter
	add [C], 48			;The printed char should be a number, add 48 to convert
	add I, 1			;incerement I
	set PC, loop			;loop
:lett	add [C], 55			;letter, add 55 to convert
	add I, 1			;increment I
	set PC, loop			;loop

:done	set I, POP
	set Y, POP
	set X, POP
	set C, POP
	set B, POP
	set A, POP			;POP stuff back
	set PC, POP			;RETURN
		
:data	dat "aaaa" 			;only way i can think of to reserve 4 words