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Index > Macroinstructions > [fasmg] get data size of struc element

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zhak



Joined: 12 Apr 2005
Posts: 490
Location: Belarus
zhak
I extended simple struct macro to be able to pass data sequences.
Code:
macro struct? name
  macro end?.struct?!
      end namespace
        local a, i, n, t
        a = 0
        i = 0
        t equ
        irp def, args
          match name:type <value, def
            if a = 0
              store value:type at .name
              n equ .name
              t equ type
              i = 0
              a = 1
            else
              err "Sequences should be in 'name:type <n1,n2,...,nx>' format"
            end if
          else match value>, def
            if a = 1
              store value:t at n + (i + 1) * t
              a = 0
            else
              err "Sequences should be in 'name:type <n1,n2,...,nx>' format"
            end if
          else match name:value, def
            store value at .name
          else match value, def
            if a = 1
              i = i + 1
              store value:t at n + i * t
            else
              err "Values should be passed in 'name:value' format"
            end if
          end match
        end irp
    end struc
    virtual at 0
      name name
      sizeof.name = $
    end virtual
    purge end?.struct?

  end macro

    struc name args&
      label . : sizeof.name
      namespace .
end macro
    

But to do this, I have to pass data type for the sequence:
Code:
_my MY a:1, b:word <1,2,3>
    

Is it possible to retrieve data size from struc element to re-use it without the need to specify it explicitly?
Post 10 Feb 2017, 15:11
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7750
Location: Kraków, Poland
Tomasz Grysztar
If you define a label with associated size, like:
Code:
data1 db ?
label data2 : word    
you can then extract this size with "metadata 0" operator:
Code:
dd data1 metadata 0 ; 1
dd data2 metadata 0 ; 2    
There is also an unary operator "sizeof" which is simply an alias for "metadata 0":
Code:
dd sizeof data1 ; 1
dd sizeof data2 ; 2    


As you may already know (because the basic "struct" macro uses it) when STORE directive has no declared size, the size that is associated with address is then used:
Code:
label name : type
store value : type at name
store value : sizeof name at name ; same as above but uses "name" only
store value at name               ; also the same result    
(note that this is not compatible with fasm 1, where STORE with no size specified used the default size 1).
Post 10 Feb 2017, 17:02
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zhak



Joined: 12 Apr 2005
Posts: 490
Location: Belarus
zhak
Thanks Tomasz!

Another question: how can I pull first param value outside match?
From the above macro,
Code:
match name:value, def
  . . .
end match
; here want to use name
    

I tried equ, define, and even =, but none worked.
Something like
Code:
local param
;define param
match name:value, def
  param equ .name ; or redefine param name
end match
display sizeof param ;or .param
    
Post 11 Feb 2017, 00:07
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7750
Location: Kraków, Poland
Tomasz Grysztar
Yes, it's the EQU (or DEFINE) that should work for this purpose:
Code:
match name:value, x:1
  name dd value
  param equ name
end match 
display '0' + sizeof param    
(this is a working snippet, it assembles all by itself).
But sometimes you may need to extract the value of symbolic variable into a parameter with MATCH:
Code:
match name:value, x:1
  param equ name
  v = value
end match

match name, param
  name dd v
end match

display '0' + sizeof param    
(attempting to define it as "param dd v" without MATCH would try to define symbol called "param" instead of "x" - the symbolic variables are automatically evaluated only inside the expressions in arguments to directives).
Post 11 Feb 2017, 10:49
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