Align to Boundary

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Tommy

Joined: 17 Jun 2003
Posts: 489
Location: Norway

Tommy 16 Sep 2005, 19:51

align ebx,16 => align value of EBX to the 16th boundary...

Code:

macro align reg,bound {
  if reg in <eax,ecx,edx,ebx,esp,ebp,esi,edi>
    ; 32-bit
    add reg,bound-1
    and reg,0ffffffffh-(bound-1)
  else if reg in <ax,cx,dx,bx,sp,bp,si,di>
    ; 16-bit
    add reg,bound-1
    and reg,0ffffh-(bound-1)
  else
    ; 8-bit
    add reg,bound-1
    and reg,0ffh-(bound-1)
  end if
}

16 Sep 2005, 19:51

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 18 Sep 2005, 23:24

this is kind of macro which IMHO isn't very good to use in real coding. you don't align registers often, and "and eax,FFFFFFF0h ;align to 16 bytes" is more readable than searching source for what exactly overloaded align does.
ps: check for [] type of "reg", eg. "align [aaa],16"

18 Sep 2005, 23:24

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8353
Location: Kraków, Poland

Tomasz Grysztar 18 Sep 2005, 23:30

And why not just:

Code:

macro align reg,bound { add reg,bound-1
                        and reg,not(bound-1) }

18 Sep 2005, 23:30

Tommy

Joined: 17 Jun 2003
Posts: 489
Location: Norway

Tommy 19 Sep 2005, 06:11

Thnx Tomasz (didn't think of it)...

19 Sep 2005, 06:11

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20333
Location: In your JS exploiting you and your system

revolution 19 Sep 2005, 08:05

Better is one that allows the use of normal align also

Code:

macro align reg,[bound] {
if ~ bound eq
add reg,bound-1 
and reg,not(bound-1)
else
align reg
end if
}

BTW: What happens for this?

Code:

align eax,3

Perhaps you should also check if the bound is a power of 2?

So now we modify the macro to this.

Code:

macro align reg,[bound] {
if ~ bound eq
add reg,1 shl bound-1 
and reg,not(1 shl bound-1)
else
align reg
end if
}

19 Sep 2005, 08:05

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