ASM indentation style

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

Moderator: Moderators

Posts: 72
Joined: Wed Apr 04, 2018 7:29 pm
Location: Montreal, Canada

ASM indentation style

Post by bleubleu » Fri Dec 28, 2018 7:35 pm


I hate how I indent my assembly code. I helps readability, but I am very inconsistent.
Basically I tend to increase the indent when it feels like a proper branch or a loop (as if it would be one in higher level languages like C) but I tend not to indent when it is simply a random jump target.
I don't want to use unnamed labels. I like how I see my labels in the debugger, it is very useful to me.

This is what it looks like, and I dont like it!

Code: Select all

some_loop: ; this is a loop, so i tend to indent here.

	lda test
	bmi test_is_negative

	test_is_positive: ; feels like a legit branch, so both if/else are indented.
		inc test_is_minus
		jmp resume
		dec test_is_minus

	resume: ; this label feels ugly.
	dec count
	bne some_loop
How do you guys do it? Again, i dont want unamed labels.


Formerly 43110
Posts: 390
Joined: Wed Feb 05, 2014 7:01 am
Location: us-east

Re: ASM indentation style

Post by JRoatch » Fri Dec 28, 2018 8:51 pm

What about it in particular that you don't like? That's there indenting at all? or that the indenting dosn't intuitively hint at execution structures (like if else, while etc)?

From what I seen, what you have is how other people indent their code, if they indent 6502 asm at all.

The most common style is essentially unindented:

Code: Select all

    lda test
    bmi test_is_negative
    inc test_is_minus
    jmp end_test
    dec test_is_minus
    dec count
    bne some_loop
As for myself here's how I go about indenting things (you can adopt as much or as little of this as you want)

Code: Select all

; two spaces for each intent level due to me sometimes being in 3 or 4 levels deep in IF and LOOPS
subroutine:  ; top level for global label intended to be called by outside code
  pha  ; pha and pla introduces a indent level
    lda test1
    beq skip_everything  ; forward branches inside a subroutine indents forward until the label
      ldy count
      loop:  ; labels from backward branches indents until the branch
        lda test3
        bmi else_is_negative  ; this is a if else structure which has a somewhat special way of indenting
        is_positive:  ; A label to remind me what the condition was to get here, also makes it easier to reorder blocks of code
          inc sum
        jmp endif  ; outside of the if else structure I generally unindent jmp and rts. Even if it's in the middle of the code.
          dec sum
      beq loop
      lda sum
      beq no_save
        sta saved_sum
      no_save:  ;  all branches goes to unique labels, even if they are at the same PC.
rts  ; rts ends the subroutine block so I unindent.
From then I occasionally add a blank line between sections of code that otherwise don't have branches.

There are exceptions of course, especially when I optimize branch ordering for speed.

Edit: Spelling corrections
Last edited by JRoatch on Sat Dec 29, 2018 7:56 am, edited 2 times in total.

User avatar
Posts: 2329
Joined: Tue Jun 24, 2008 8:38 pm
Location: Fukuoka, Japan

Re: ASM indentation style

Post by Banshaku » Fri Dec 28, 2018 9:09 pm

I usually don't indent since this is something I'm used for high level language like c, java etc. For asm, I tend to put blank lines to separate group of action of if it refer to a specific processing.

Here an example of a helper function (that is a little long) used while fading the palette at a specific step. The reason a take a longer one is to show what I mean by blank lines:

Code: Select all

; Helper function that apply a value on the palette for a specific range
; note:
; - most locals are set from calling function
; - 'A' contains decrement
.proc subFadeStep
;---------------- Parameters definitions ----------------
.scope local
    paletteAdr  = zpTemp     ; adress of source palette
    steps       = zpTemp+2   ; how many color to change
    start       = zpTemp+3   ; where to start in palette
    decrement   = zpTemp+4   ; to remove by how much
    waitFrames  = zpTemp+5   ; How many frame to wait at the end of 1 step
    useVBlank   = zpTemp+6   ; use vblank instead of nmi for waiting    

    sta local::decrement            ; save decrement from calling function

    ldx local::steps                ; load counter
    ldy local::start                ; load target start position

    lda #$00
    sta zpPaletteUpdateFlag         ; set flag to disable palette update

    lda (local::paletteAdr),y       ; load color from buffer
    sbc local::decrement            ; if carry clear, out of bound
    bcs colorNotOutsideBound        ; no, was not, use new color value
    lda #$0F                        ; when outside bound, set to black by default

    cmp #$0D                        ; Edge case: check if blacker than black
    bne notBlackerThanBlack         ; no it's not, skip that step
    lda #$0F                        ; it is, use $0F instead

    sta palBuffer, y                ; store in buffer for nmi
    iny                             ; go next step in buffer
    dex                             ; reduce counter
    bne loop                        ; not end of counter? do next color

    inc zpPaletteUpdateFlag         ; set flag to update palette

    ldx local::waitFrames           ; load frames to wait

    lda local::useVBlank            ; check which way to wait
    bne whileWaitVBlank             ; use vblank intead

    jsr subWaitNmi                  ; Use NMI to wait frame

    bne whileWaitNmiFrame           ; If not 0, still some frames to wait


    jsr subWaitVBlank               ; Use vblank instead

    bne whileWaitVBlank             ; If not 0, still some frames to wait


But formatting code is something personal and that you define with time. The only time you will want everyone to make it all the same is while working at a company: if you don't, trying to read other people code and managing it will be quite hell ^^;;

Posts: 21841
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)

Re: ASM indentation style

Post by tepples » Fri Dec 28, 2018 9:14 pm

I generally use what amounts to the same style as bleubleu, with 2 spaces, without dedenting jump/branch the way JRoatch does. I even built a preprocessor for RGBASM (Game Boy assembler), which expects all labels to start in column 1, to be able to keep this indent style.

Indentation is slightly more important in assembly than in C, as I'm not aware of any automated way to determine block structure in assembly. In C, on the other hand, there exist numerous indent filters.

User avatar
Posts: 549
Joined: Thu Mar 31, 2016 11:15 am

Re: ASM indentation style

Post by pubby » Fri Dec 28, 2018 10:22 pm

The whole concept of indenting feels misguided. Assembly doesn't nest, and the control flow it produces often jumps around in a way that can't be represented with indentations (i.e. the control flow is irreducible). The moment you break the indentation rules for an unusual jump, the advantage of indenting goes out the window because it's not consistent anymore.

Posts: 21841
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)

Re: ASM indentation style

Post by tepples » Fri Dec 28, 2018 10:35 pm

Indentation resembling that associated with block-structured languages at least shows readers of your code that you're trying to adhere to the principles of structured programming with early exit to the extent possible in assembly language.

User avatar
Posts: 4216
Joined: Sun Sep 19, 2004 9:28 pm
Location: A world gone mad

Re: ASM indentation style

Post by koitsu » Fri Dec 28, 2018 11:50 pm

bleubleu wrote:How do you guys do it?
Simple: I don't.

User avatar
Posts: 7718
Joined: Sun Jan 22, 2012 12:03 pm
Location: Canada

Re: ASM indentation style

Post by rainwarrior » Sat Dec 29, 2018 12:19 am

pubby wrote:Assembly doesn't nest, and the control flow it produces often jumps around in a way that can't be represented with indentations (i.e. the control flow is irreducible). The moment you break the indentation rules for an unusual jump, the advantage of indenting goes out the window because it's not consistent anymore.
I don't believe there is a way to indent assembly in any 100% consistent way.

However, I feel there's a lot of value in visual information from indentation, and just because some cases won't fit a structure exactly doesn't mean that it can't be helpful to indicate cases that do, and can even apply in a useful way to cases that don't quite.

In most cases, I add an indent after a branch, and that indent will end at the end of the code it jumps to. For "if, else" style, there's a brief break in the indent at the else. This makes the length of the branch and its structure instantly readable visually, and I can quickly skim to the end of the structure without having to read the code in between. These two cases covers probably 95% of indents in my assembly code. Especially when nesting simple decision branches within a larger if/else, this make it very easy to see the hierarchy and extent of what's happening there. (typical example)

Sometimes it gets weird, and I'll make a decision whether to indent or not. It's not necessarily consistent with the rest of my code, but this is because assembly code structures are not consistent. I simply make a decision about how I think I would best read the indent when I'm trying to come back to this code in the future, and leave it that way. Sometime that means a flat/unindented style. Sometimes that means indents that don't match other uses quite. Sometimes that means an extra comment or two to clarify.

The bottom line is that the indents are there to make something easy to read. They're not information for a computer or a compiler, so they don't need to fit some formal and absolute definition of structure. The tabs are merely a visual tool.

If I was writing code that was part of a library for a company that is selling the code itself as the product, however, and not something for my own use, most likely a non-indented style would be mandated for assembly, partly for the consistency, but mostly for traditional practice. It is simply the "standard" appearance of assembly code, and probably worth using as a lowest-common-denominator that nobody would be able to say is an unexpected or irregular practice. This usage case is very different than anything I've done for the NES though.

User avatar
Posts: 11520
Joined: Sat Feb 12, 2005 9:43 pm
Location: Rio de Janeiro - Brazil

Re: ASM indentation style

Post by tokumaru » Sat Dec 29, 2018 12:44 am

Yeah, I don't indent ASM code either. One of the advantages of using assembly is that you're not bound to the constructs of higher-level languages, so you can optimize your code in ways that are not possible in other languages. Not that I'm suggesting everyone starts writing messy spaghetti code, you should definitely try to adhere to some sort of programming style that makes sense to you, so that if you're coherent enough, your own code will always make sense to you, it's just that imposing formatting limitations that weren't even invented for this type of language can't really end well, can it?

What makes assembly particularly hard to indent is the fact that there are often several paths to a given set of instructions. In higher-level languages you have to nest all the different decisions and each one will select whether to go deeper or not, but in assembly you can move freely to any depth, different paths can merge later, it's a completely different story.

Instead of using indentation and trying to artificially make my program look like it has a structure it doesn't, what I do is write comments at the top of each block of related instructions explaining the conditions that lead to the execution of that block. I always start a new block with instructions that are the target of significant jumps/branches, so I can easily tell the paths that the logic can take. This means that I still have easily discernible blocks of logic, the difference is that they're not nested, I can move freely from block to block.

Posts: 9027
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: ASM indentation style

Post by lidnariq » Sat Dec 29, 2018 1:10 am

Without writing a huge essay, I'll just summarize my asm style as:
I use vertical whitespace instead of horizontal whitespace to signal semantics.

Posts: 786
Joined: Tue Feb 07, 2017 2:03 am

Re: ASM indentation style

Post by Oziphantom » Sat Dec 29, 2018 5:37 am

Code: Select all

	jsr inter_waitRaster
	jsr inter_moveOthersLeft
	jsr inter_movePlayerLeft
	jsr inter_animateSpritesNotPlayer
	dec IMZ_SpriteTimer
	bne +
		lda screenSprID0	
		cmp #149+kSprBase	
		beq _doneTrample	
			lda $d001
			adc #2
			sta $d001
			inc screenSprID0					
		lda #7			
		sta IMZ_SpriteTimer				
+  ldy #3*2
	jsr inter_compareSpriteYXLessThan
	bcs -
Is the normal way I do it. Once you get into the
A -> C,D
B -> C
C -> E,F
E -> G
F -> B
kind of chains it starts to become meaningless to do the indents for all of it. Putting an empty line after a hard jmp, effective jmp or rts is also normal for me. Sometimes you can fix it by making some parts of the code into a macro/segment and using that to keep the structure clearer, but then its obfuscated by having code hidden behind macros.

Getting into this discussion on the C64 forums usually gets heated. With people declaring the C64 doesn't have a TAB key for a reason.. to which one can shoot back with the more evolved C128 does ;)

User avatar
Posts: 2329
Joined: Tue Jun 24, 2008 8:38 pm
Location: Fukuoka, Japan

Re: ASM indentation style

Post by Banshaku » Sat Dec 29, 2018 8:38 am

Like Oziphantom said, it becomes quite "religious" to some degree so its better to not go to deep into it ^^;; There is no perfect way but the one you feel comfortable with it. The only time you need to adhere to a style is when you work with a group of individual.

User avatar
Posts: 673
Joined: Sat Jan 09, 2016 9:21 pm
Location: Central Illinois, USA

Re: ASM indentation style

Post by gauauu » Sat Dec 29, 2018 12:04 pm

I do like Rainwarrior - I indent when it helps readability. I'm not consistent with any rule, I just do whatever makes that chunk of code easier for me to read later. Sometimes that means indenting like C. Sometimes it just means lots of comments and vertical spacing.

Posts: 153
Joined: Wed Nov 30, 2016 4:45 pm
Location: Southern California

Re: ASM indentation style

Post by Garth » Sat Dec 29, 2018 6:22 pm

I agree with many of the points above (although not all). I indent to make conditionals and loops obvious, and also things like what's between a PHA and PLA for example. I always indent at least three spaces. One or two spaces are just enough to make it look like you just got really sloppy at vertical alignment, whereas three is pretty clear; or if the indented portion is pretty long, I might go for four, rarely five.

Blank lines are also important to readability. I hate trying to read code from the 1970's and early 80's where all the mnemonics start in the same column and there are no blank lines to visually group sets of instructions like punctuation and paragraphs do in prose.

Several years ago I realized there's a way to do nestable program flow-control structures in assembly macros without labels, even if the assembler does not provide a way to have variable arrays in the assembler itself and index into them in order to have the needed stack in the assembler itself. Since then, I've been enjoying assembly language a lot more and I've become more productive and gotten fewer bugs. In most cases, the macros assemble exactly the same thing you would do by hand, but they make the source code more readable and maintainable. In some cases you'll actually get better efficiency from the macros, just because there's greater visibility of what you're doing, which helps you spot inefficiencies in your approach. Use of the structure macros still allows the use of labels so you can jump into the middle of a program structure; but I don't do that without a really good reason. My article on it is at . There are some longer usage examples in the last 40% of my page on multitasking at, and more explanation of how the assembler does them in the program-structure chapter of my 6502 stacks treatise, at .

For your original routine above, I might write it this way:

Code: Select all

        LDA  test
            INC  test_is_minus
            DEC  test_is_minus
        DEC  count
The assembler's output would be the same. (Is "test" an input port? Or perhaps interrupts could be changing it while this loop is running?) lots of 6502 resources

Posts: 112
Joined: Tue Oct 16, 2018 5:46 am
Location: Gothenburg, Sweden

Re: ASM indentation style

Post by pwnskar » Wed Jan 02, 2019 10:02 am

I sort of follow what I'm used to from other languages just because it makes things easier for me to read and wrap my head around. I'm not super consistent with it but for me that's not really the point. I just want to be able to read and understand what I'm doing with the code, so with that I usually do a lot of comments and little "TODO" notes.

I'll follow Banshaku's example and show you my take on the same task. :)

Code: Select all


	; a = how much to subtract from currently loaded palette.
	; TODO: if the palette pointers have not been set yet, do something to handle that.
	ldx palette_bkg_ptr_lo
	ldy palette_bkg_ptr_hi
	stx curr_pointer_lo
	sty curr_pointer_hi
	ldx #15
	jmp BufferOffsetPalette
	; a = how much to subtract from currently loaded palette.
	ldx palette_sprites_ptr_lo
	ldy palette_sprites_ptr_hi
	stx curr_pointer_lo
	sty curr_pointer_hi
	ldx #31
	; x = palette_buffer end index
	pha	; how much to subtract
	lda nmi_flags
	sta nmi_flags
	ldy #15
		pha		; push this for next loop iteration
		adc (curr_pointer_lo), y	; offset palette value with a
		pha							; push this so we can use a for some logic
		; first, lets knock down all $xE and $xF to $xD
		and #%00001111
		cmp #$0e
		bcc @no_xE
			; we've determined that the value must be $xE or $xF
			; knock it down to $xD
			pla				; retrieve offset palette value
			and #%11110000
			ora #%00001101
			jmp @xEset
			pla				; retrieve offset palette value
		; TODO: determine if the offset was positive or negative.
		; we could do that by temporarily storing a in the buffer and digging out the initial offset by pla
		sta palette_buffer, x
		pla		; retrieve original offset value
		pha		; and push it again for next loop itteration.
		bpl @offsetispositive
			lda palette_buffer, x
			cmp #$20
			bne @not20
				lda #$10
				sta palette_buffer, x
				;jmp @offset_adjusted_by_direction
			jmp @offset_adjusted_by_direction
			lda palette_buffer, x
			cmp #$1d
			bne @not1d
				lda #$2d
				sta palette_buffer, x
				jmp @offset_adjusted_by_direction
			cmp #$2d
			bne @not2d
				lda #$00
				sta palette_buffer, x
				;jmp @offset_adjusted_by_direction
		lda palette_buffer, x
		cmp #$3d+1				; so now we check if any value goes above 3d (out of range) and cap it to either 30 or 0d
		bcc @nocap				; is the value above 127?
			cmp #0
			bpl @nocap1
				; if the offset was negative, this is our stop
				lda #$0d
				jmp @nocap
				; this is where we end up if the offset was positive
				lda #$30
		sta palette_buffer, x
		cpy #$ff
		bne @offsetloop
	pla		; clean stack from original a value
	; TODO: patch all sprite opacity buffers with that of the background palette buffer
	lda palette_buffer
	sta palette_buffer+16	; seems just patching the first entry of the sprite palette buffer is enough..
	lda nmi_flags
	sta nmi_flags
I'm surprised so many people seem to not do indentation! :) For me that simply wouldn't work. My mind needs some visual aide even to just help my eye find it's way back to the right spot on the screen when going back and forth between all my source files.

Post Reply