Macro concatenation and repeat problem

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Plue

Joined: 15 Dec 2005
Posts: 151

Plue 08 Dec 2007, 19:42

Code:

macro MK NUM {
  mov [v_a], NUM
  ; show v_a here
}

repeat  16
        MK %
end repeat

That code works perfectly, and shows the numbers from 1 to 16. But when I do this:

Code:

macro MK NUM {
  l#NUM:
}

repeat  16
        MK %
end repeat

I get that the symbol is already defined. Which it shouldn't be, and isn't if I unroll the repeat manually:

Code:

macro MK NUM {
  l#NUM:
}

MK 1
MK 2
MK 3
MK 4
MK 5
MK 6
...

What's wrong?

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08 Dec 2007, 19:42

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 08 Dec 2007, 19:55

Unrolling would be this:

Code:

l%:
l%:
l%:
l%:
l%:
l%:
...

"repeat" does not instantiates the macro multiple times, it occurs only once at preprocessing time, so, what you need is this

Code:

loco@athlon64:~/Desktop$ cat plue.asm
macro MK NUM {
  l#NUM:
} 

rept 6 count
{
  MK count
}

push l1 l2 l3 l4 l5 l6 ; Just to test that the symbols are defined
loco@athlon64:~/Desktop$ fasm plue.asm
flat assembler  version 1.67.24  (16384 kilobytes memory)
1 passes, 12 bytes.

08 Dec 2007, 19:55

Plue

Joined: 15 Dec 2005
Posts: 151

Plue 08 Dec 2007, 20:05

What's the use for repeat if rept does it better? Why isn't the first repeat unrolled to this?
mov [v_a], %
mov [v_a], %
mov [v_a], %
mov [v_a], %
mov [v_a], %
mov [v_a], %

08 Dec 2007, 20:05

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 08 Dec 2007, 20:28

The problem is that the concatenation occurs at preprocessing time only so the assembler layer is not able to create labels attaching the value of % to them. The rept however does textual repetition of the macro so it is instantiated 6 times while the repeat assembler directive does not do any textual repetition, just interpret the lines again incrementing the output.

To summarize, this is the text that the assembler receives with rept

Code:

 l1:
 l2:
 l3:
 l4:
 l5:
 l6:

And this with repeat

Code:

repeat 6
  l%:
end repeat

The rule is that if the macro does not define any label you can use "repeat" with them, otherwise you need the less flexible and more memory consuming (at compile time) "rept".

And concerning your other code with repeat is this

Code:

repeat 6
  mov [v_a], %
end repeat

And with rept 6, count is

Code:

; rept 6, count {MK count}
  mov [v_a], 1
  mov [v_a], 2
  mov [v_a], 3
  mov [v_a], 4
  mov [v_a], 5
  mov [v_a], 6

This time the output will be the same, but the source text that the assembler receives is different.

08 Dec 2007, 20:28

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8267
Location: Kraków, Poland

Tomasz Grysztar 08 Dec 2007, 21:16

Note: when you've got a situation where both REPT and REPEAT will be good for your purpose, choose REPEAT, as it will eat less memory during the compilation, and will assemble a little bit faster, too.

08 Dec 2007, 21:16

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