Expanding Macros

[savage]

Okay, I think I have it working, I really liked your first version better so I'm using that, but I can't figure out how to make things like (2+2) reduce to 4, because I don't want my variable named "const_2+2" for example

[Ossa]

Okay, I think I have it working, I really liked your first version better so I'm using that, but I can't figure out how to make things like (2+2) reduce to 4, because I don't want my variable named "const_2+2" for example

"% is your friend"  :bg

Once again from the MASM Programmer's Guide (I quoted the next section last time we talked about macros - here):

Converting Numeric Expressions to Text

The expansion operator can convert numbers to text. The operator forces immediate evaluation of a constant expression and replaces it with a text value consisting of the digits of the result. The digits are generated in the current radix (default decimal).

This application of the expansion operator is useful when defining a text macro, as the following lines show. Notice how you can enclose expressions with parentheses to make them more readable:

Code Select Expand

a       TEXTEQU <3 + 4>         ; a = "3 + 4"
c       TEXTEQU %(3 + 4)        ; c = "7"

When assigning text macros, you can use numeric equates in the constant expressions, but not text macros:
 

Code Select Expand

num     EQU     4               ; num = 4
numstr  TEXTEQU <4>             ; numstr = <4>
a       TEXTEQU %3 + num        ; a = <7>
b       TEXTEQU %3 + numstr     ; b = <7>
 
The expansion operator gives you flexibility when passing arguments to macros. It lets you pass a computed value rather than the literal text of an expression. The following example illustrates by defining a macro

Code Select Expand

work    MACRO   arg
    mov ax, arg * 4
ENDM
 
which accepts different arguments:
 

Code Select Expand

        work    2 + 3           ; Passes "2 + 3"
                                ; Code: mov ax, 2 + (3 * 4)
        work    %2 + 3          ; Passes 5
                                ; Code: mov ax, 5 * 4
        work    2 + num         ; Passes "2 + num"
        work    %2 + num        ; Passes "6"
        work    2 + numstr      ; Passes "2 + numstr"
        work    %2 + numstr     ; Passes "6"
 
You must consider operator precedence when using the expansion operator. Parentheses inside the macro can force evaluation in a desired order:
 

Code Select Expand

work    MACRO   arg
    mov ax, (arg) * 4
ENDM

        work    2 + 3           ; Code: mov ax, (2 + 3) * 4
        work    %2 + 3          ; Code: mov ax, (5) * 4
 
Several other uses for the expansion operator are reviewed in "Returning Values with Macro Functions," later in this chapter.

So if all else fails, a dummy string at the start that uses the expansion operator on the passed string would do it.

Ossa

[savage]

Okay, exactly whatI think I was looking for, thanks Ossa.
So the dummy string is used along with % in order to reduce expressions. 
:dance:

Gotcha.

Thanks again for being so quick.

[jj2007]

     If you code the MASM directive .LISTMACROALL at the beginning of your source code, the calling sequence of nested MACROS, and the variables within will be printed in the listing.  Ratch

Could it be .listall? It yields some more expansion code than .listmacroall, although it is still far from satisfactory. I am also looking for more transparency on my macros...