Concat constant value to symbol in a macro (fasm 1.73.30)

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BismuthGlass

Joined: 08 Mar 2022
Posts: 4

BismuthGlass 08 Mar 2022, 17:01

Hello everyone,

I've been recently trying to make the switch over from nasm to fasm, and something I use a lot over at nasm is the generation of unique global labels through appending a variable value to a label name. I was trying to figure out how to do this in fasm, but I just can't seem to do it, and I can't find any info on it either. Here's an example of what I'm trying to write:

Code:

macro strtbl name, [string] {
    common
        local variable
        variable = 1
    forward
        label name#variable
        db string, 0
        variable = variable + 1
}

strtbl lbl, 'abc', 'dfg', 'eaf'

So the idea is that this would generate:

Code:

label lbl1
db 'abc', 0
label lbl2
db 'dfg', 0
label lbl3
db 'eaf', 0

Is there a way to achieve this?

Also, on an unrelated note, should I be using FASM1 at all, or should I just use FASMG? I am somewhat aware of the differences, but I can't really find a consensus on what people usually use, and the reasons to use FASM1 over the newer FASMG.

Thank you in advance.

08 Mar 2022, 17:01

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8358
Location: Kraków, Poland

Tomasz Grysztar 08 Mar 2022, 18:26

Because fasm 1 has a separate preprocessing stage, you need to use a preprocessor-time variable and REPT directive to make a computed token. The variables defined with "=" are assembly-time, so they are of no use here (preprocessor sees lines like "variable = variable + 1" as just a raw text to pass to the assembly stage).

Your macro should therefore look like this:

Code:

macro strtbl name, [string] {
    common
        local variable
        variable equ 1
    forward
        rept 1 v:variable
        \{
            label name\#v
        \}
        db string, 0
        variable equ variable + 1
}

strtbl lbl, 'abc', 'dfg', 'eaf'

To make sure that you get what you wanted, you can generate a symbols file (with "-s" switch in command line) and then use PREPSRC tool (from the TOOLS directory) to see the output of the processor that is then passed to the assembler:

Code:

; variable?0
;variable?0 equ 1

;rept 1 v:variable?0
;{
; label lbl#v
;}
label lbl1
db 'abc',0
;variable?0 equ 1+1
;rept 1 v:variable?0
;{
; label lbl#v
;}
label lbl2
db 'dfg',0
;variable?0 equ 1+1+1
;rept 1 v:variable?0
;{
; label lbl#v
;}
label lbl3
db 'eaf',0
;variable?0 equ 1+1+1+1

BismuthGlass wrote:

Also, on an unrelated note, should I be using FASM1 at all, or should I just use FASMG? I am somewhat aware of the differences, but I can't really find a consensus on what people usually use, and the reasons to use FASM1 over the newer FASMG.

I have written a short summary of potential reasons in the migration guide. In general, unless you need a really fast assembly of lots of x86 code, you should find fasmg more capable. With fasmg a macro doing the same thing could look like:

Code:

macro strtbl name, strings&
        iterate string, strings
                label name#%
                db string, 0
        end iterate
end macro

strtbl lbl, 'abc', 'dfg', 'eaf'

08 Mar 2022, 18:26

BismuthGlass

Joined: 08 Mar 2022
Posts: 4

BismuthGlass 09 Mar 2022, 10:37

Thanks for the suggestions. I must admit that fasmg looks very scary, but reading through the examples and the manual it has a lot of cool features, and I really like the "everything is a macro and nothing is sacred" philosophy. It seems like the kind of thing I've been looking for, so I'll give it a go.

09 Mar 2022, 10:37

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