PureBasic Forums - English

Posted: **Mon Apr 23, 2012 2:00 pm**

I wonder if there is a function that evaluates the entered value in a macro?

Explaining with an example will clarify my question.
This works:

Code: Select all

Macro Goto(x)
    Goto x
EndMacro


Goto(There)
End


There:
Debug "We are there!"
End

Now, imagine that I want to put the label in a variable, and then the macro should evaluate the value A, to get "There" instead of using "A"
So, this does not work:

Code: Select all

Macro Goto(x)
    Goto x
EndMacro


A.s="There"
Goto(A)
End


There:
Debug "We are there!"
End

I was thinking of someting like this: (but I don't know if this exists)

Code: Select all

Macro Goto(x)
    Goto Eval(x)
EndMacro

to transform "x" in "There", so the macro should read "Goto There".

Any suggestion?
Thanks

PS: if there is a way, then I have a little surprise for you all !

Posted: **Mon Apr 23, 2012 2:49 pm**

a Macro is not a function (procedure).
Macros are create on compile time, not on run time.
So you can't evaluate it!

Code for your axample:

Code: Select all

Global ASMLabelPointer
Global NewMap Label.i()

Macro Goto(x)
  ASMLabelPointer = Label(x)
  !JMP [v_ASMLabelPointer]
EndMacro


Label("Label_1") = ?Label_1
Label("Label_2") = ?Label_2
Label("Label_3") = ?Label_3


Define A.s = "Label_2"
Goto(A)



Label_1:
Debug "We are at Label_1!"
End 

Label_2:
Debug "We are at Label_2!"
End 

Label_3:
Debug "We are at Label_3!"
End

Posted: **Mon Apr 23, 2012 3:24 pm**

Or, if you need to determine the destination on the fly (not in compile time) assign the destination to a pointer variable (i.e. *a) and then gosub or goto the pointer value:

Code: Select all

Goto start 

one:
	Debug 1
Return

two: 
	Debug 2
End


start:

; this is like a=one : gosub(a)
*a = ?one
! call [p_a]


; this is like a = two : goto(a)
*a = ?two
! jmp [p_a]

Of course you can turn that into macros...

Posted: **Mon Apr 23, 2012 3:35 pm**

VERY VERY interesting, Stargate!

It is an excellent start-idea.

a Macro is not a function (procedure).
Macros are create on compile time, not on run time.
So you can't evaluate it!

I know, hence my question...

I don't think I can do a Goto Label_2 with a Procedure.

The "little surprise" I was trying to make, is the insertion of the Gosub in the procedures. Gosub exists in PB, but works only in the main program, outside the procedures.

I am trying that because I am missing the Gosub. Of course, I can use procedures for repeating operations, but then I need to bring all the variables to that procedure, and that's often a lot of work. The only solution is of course to use Goto.
Stargate, maybe you can help? Because I don't know Assembler at all.
Here is the basic idea:

Code: Select all

Macro Gosub(x,y)
    Back.s=Eval(y)
    Goto x
EndMacro


Macro Return()
    Goto Back.s
EndMacro


Debug "Start!"
Gosub(SubVerify,Cont) : Cont: : Debug "Continue the program after GOSUB"
End


SubVerify:
Debug "Verification routine..."
Return()

You see here that the problem is the Back.s variable. I need to evaluate the value of Back.s, in order to return to the label Cont:, when the subroutine is done.
Sure, we must then think further, because we can have nested Gosub's....

Posted: **Mon Apr 23, 2012 3:38 pm**

Tenaja wrote:
; this is like a=one : gosub(a)
*a = ?one
! call [p_a]

Hey Tenaja, maybe that's the solution?! I need to try that!

Posted: **Mon Apr 23, 2012 3:52 pm**

Yay !!! Tenaja, I could use your ASM code!

Code: Select all

Macro Gosub(x)
    *subroutine=?x
    ! call [p_subroutine]
EndMacro


Debug "Start!"
Gosub(SubVerify)
Debug "Continue the program after GOSUB"
End


SubVerify:
Debug "Verification routine..."
Return

It seems that the ASM code takes the whole line, so I had to put the "Debug "Continue the program after GOSUB" on a new line, instead of the same line. This is apparently not possible:

Code: Select all

Gosub(SubVerify) : Debug "Continue the program after GOSUB"

This is a minor problem, a pity, but it is a rule that we need to remember. But the Gosub works!!!
Thank you sooo much!!!

Posted: **Mon Apr 23, 2012 5:32 pm**

charvista wrote: I am trying that because I am missing the Gosub. Of course, I can use procedures for repeating operations, but then I need to bring all the variables to that procedure, and that's often a lot of work. The only solution is of course to use Goto.

Glad to help... but it will not change the dilemma you mention here. You have to understand scope. If you can't access a var in a proc, then a goto to a different code section will not change that. The way local variables work is by an offset from the stack pointer. The offset is based on when the proc is entered, and any changes to the stack (either with Gosub's, other proc calls, or any other means) will cause the references to change. Consider this "pseudo" code:

Code: Select all

Procedure Proc1()
	Protected x   ; x is "stackoffset + 0"
LabelAtProc1:
		x= 1
EndProcedure
	
Procedure Proc2:
	Protected y    ; y is also "stackoffset + 0"
	Protected z    ; z is "stackoffset + 4" (assuming 32-bit os and y is a 4-byte integer)
	Goto LabelAtProc1 ; (using new asm code)
EndProcedure

While incomplete, it serves the purpose of explaining that when you arrive at the goto label, the "x=1" command will actually change the Y variable from the originating Proc! This is because both procs use (stack) as a reference for the first variable, and a goto does not change the stack. For the second local var, it is (stack + (var 1 size)) for the second variable, and keep adding offsets for each new local.

Anyway, if you are just trying to save the work of copying variables, then you have two options: Make all of those vars Global, or put the code section in another Proc. You'll just have problems if you try to execute a "subroutine" in the middle of a proc if that sub references any local vars. There is a reason Fred prohibits Goto and Gosub in a proc, and it is to prevent code screwups.

Posted: **Mon Apr 23, 2012 10:17 pm**

charvista (myself) wrote:
[...] I can use procedures for repeating operations, but then I need to bring all the variables to that procedure [...]

Yes Tenaja, what I wrote could be understood in two manners. I believe that you understood that I would like to do a Goto/Gosub from a procedure to another procedure like in your quick example. But I mean this: I need to bring (pass) all the variables to that procedure (through the argument variables)

So, instead of including all the variables the subroutine needs, as arguments to execute the 'subroutine', I preferred a Gosub IN THE SAME PROCEDURE. And I think that Goto's and Gosub's are perfectly legal within the procedure...

Your example to jump from Proc2() to Proc1() is luckily *not* what I am intending to do. Once, I accidentally made a Goto to a label that existed in another procedure, and the program crashed. This was very obvious!
I only use Goto inside Proc1() *OR* inside Proc2(). And now I will also use the new Gosub only inside Proc1() *OR* inside Proc2(). I hope that this way will not cause any problems.

EDIT: I discovered that your ASM does not work within procedures

Posted: **Mon Apr 23, 2012 10:57 pm**

It works if you make the var a global:

Code: Select all

Global *a

Procedure testthis()
	Protected *b
	
	
; this is like a=one : gosub(a)
*a = ?one
! call [p_a]


; this is like a = two : goto(a)
*a = ?two
! jmp [p_a]


ProcedureReturn

one:
	Debug 1
Return

two: 
	Debug 2
; End

EndProcedure

testthis()

The reason is because of the stack reference with local vars. See the output differences:

Code: Select all

; *b = ?one
  MOV    ebp,l_one
  MOV    dword [esp],ebp    ;local has stack (that's esp) offset of 0
; *c = ?two
  MOV    ebp,l_two
  MOV    dword [esp+4],ebp    ; local as the second var is esp+4, in 32-bit system.
; 
; *a = ?one
  MOV    ebp,l_one
  MOV    dword [p_a],ebp     ;global has fixed reference, p_a.

(edit: added a second local variable demo.)

Posted: **Mon Apr 23, 2012 11:05 pm**

The big problem is that the Return does not work in a procedure.... your code stops at the Return line.

Posted: **Mon Apr 23, 2012 11:20 pm**

Consider this very easy example...
I am doing a fake Gosub VerifyR, but in fact, I am doing two Goto's... If the Return worked in the procedure, then I could remove the annoying Vok: label....

Code: Select all

Global *LabelGosub
Global *LabelReturn

Macro Gosub(x,y)
    *LabelGosub=?x
    *LabelReturn=?y
    !JMP [p_LabelGosub]
EndMacro

Macro Return()
    !JMP [p_LabelReturn]
EndMacro


Procedure RandomAverage()
    
    For i=1 To 100000
        r=Random(2000-1)
        Gosub(VerifyR,Vok)
        Vok:
    Next
        
    Debug Str(H)+" times more than half"
    Debug Str(L)+" times less than half"
    
    ProcedureReturn; Quit Proc()
    
    
    VerifyR:
    If r>1000-1
        H+1
    Else
        L+1
    EndIf
    Return()
    

    
EndProcedure


RandomAverage()

Posted: **Mon Apr 23, 2012 11:49 pm**

charvista wrote:The big problem is that the Return does not work in a procedure.... your code stops at the Return line.

It does not fail on my computer, but I am running 32-bit OS. Are you on 64-bit? If so, there may be a change to the asm required.

Here is the same code slightly modified to show it does not have a problem with the return:

Code: Select all

Global *a

Procedure testthis()
	Protected *b
	Protected *c
	
	*b = ?one
	*c = ?two
	
; this is like a=one : gosub(a)
*a = ?one
! call [p_a]


; this is like a = two : goto(a)
*a = ?two
! jmp [p_a]


ProcedureReturn

one:
	Debug 1
Return

Debug "Should never get here."

two: 
	Debug 2
; End

EndProcedure

testthis()
Debug 3

Posted: **Mon Apr 23, 2012 11:58 pm**

Yes, I am on a 64-bit Windows 7 now. (This afternoon I was on a 32-bit, but I moved since then).
In your last example, it stops at line 24, that's the line that contains "Return" after Debug 1, and the error message is: "[ERROR] Invalid memory access. (write error at address 1)"
Glad that we are working together to find a Gosub solution

EDIT:

I confirm that your last example works perfectly on a 32-bit Windows 7. (I tried on my laptop)

Posted: **Tue Apr 24, 2012 12:32 am**

The easiest way is if someone experienced with 64-bit chimes in and tells us the conversion. If you don't want to wait, this is how to figure out asm from PB...

First--do you know how to view PB's asm output? If not, install this plugin in your IDE:
http://purebasic.fr/english/viewtopic.php?f=12&t=30864
I actually made a Menu button in my IDE to open it in Notepad++.

Then you write some goto's, gosub's and pointer assignments and see what the 64-bit asm codes are, so you can add them with CompilerIf's for 64-bit OS's.

Basically, putting the varname in brackets means it is an indirect call. A direct call such as "call x" is read like a "gosub x" where x is a label, but an indirect call such as "call [y]" is read like "gosub the address pointed to in y", so it requires a pointer, and not a label name. But the 64-bit opcodes are slightly different, and since I don't have a 64-bit os handy, I can't tell you the differences. I do know that you should use integer variables, since they are automatically sized.

It could be that the only difference is how Fred converts the variable name...but I don't know.

Posted: **Tue Apr 24, 2012 9:35 am**

Tested on Windows with 32bit and 64bit PureBasic:

Code: Select all

;--------------------------------------------------------------------------------------------------------
;
; START INCLUDE "Sub_SingleCall.pbi"
;
;--------------------------------------------------------------------------------------------------------

Threaded *__Sub_ReturnAddress__

Macro Sub(_name_)
    CompilerIf #PB_Compiler_Processor = #PB_Processor_x86 Or #PB_Compiler_Processor = #PB_Processor_x64
        !EndSub_Name equ __EndSub_#_name_
        !  JMP EndSub_Name
        !_sub_#_name_:
    CompilerElse
        CompilerError "Macro Sub(): unsupported processor"
    CompilerEndIf
EndMacro

Macro EndSub
    CompilerIf #PB_Compiler_Processor = #PB_Processor_x86 Or #PB_Compiler_Processor = #PB_Processor_x64
        !  JMP [p___Sub_ReturnAddress__]
        !EndSub_Name:
    CompilerElse
        CompilerError "Macro EndSub: unsupported processor"
    CompilerEndIf
EndMacro

Macro ExitSub
    CompilerIf #PB_Compiler_Processor = #PB_Processor_x86 Or #PB_Compiler_Processor = #PB_Processor_x64
        !  JMP [p___Sub_ReturnAddress__]
    CompilerElse
        CompilerError "Macro ExitSub: unsupported processor"
    CompilerEndIf
EndMacro

Macro Call(_name_)
    CompilerSelect #PB_Compiler_Processor
        CompilerCase #PB_Processor_x86
            !  MOV dword [p___Sub_ReturnAddress__],@f
            !  JMP _sub_#_name_
            !@@:
        CompilerCase #PB_Processor_x64
            !  MOV RAX, @f
            !  MOV qword [p___Sub_ReturnAddress__],RAX
            !  JMP _sub_#_name_
            !@@:
        CompilerDefault
            CompilerError "Macro Call(): unsupported processor"
    CompilerEndSelect
EndMacro


;--------------------------------------------------------------------------------------------------------
;
; END INCLUDE "Sub_SingleCall.pbi"
;
;--------------------------------------------------------------------------------------------------------




;XIncludeFile "Sub_SingleCall.pbi"

Procedure RandomAverage()

    For i=1 To 100000
        r=Random(2000-1)
        Call(VerifyR)
    Next

    Debug Str(H)+" times more than half"
    Debug Str(L)+" times less than half"
    

    ProcedureReturn; Quit Proc()
    
    
    Sub(VerifyR)
        If r>1000-1
            H+1
        Else
            L+1
        EndIf
    EndSub
    
EndProcedure


Procedure testthis()
    
    Call(one)
    Call(two)

    ProcedureReturn   ; no problem if you forget it

    Sub(one)
        Debug 1
    EndSub

    Debug "Should never get here, but it is no problem if you forget ProcedureReturn"

    Sub(two)
        Debug 2
    EndSub

EndProcedure


Procedure testthis2(arg)

    Sub(testthis2_one)
        Debug "In Sub testthis2_one"
        For i = 1 To 2
            Debug "Arg is: "+Str(arg)
            If arg = -1
                Debug "ExitSub"
                ExitSub
                Debug "after ExitSub"
            EndIf
        Next
    EndSub
    
    ;Sub(one)
        ; not allowed, Sub(one) already defined
    ;EndSub
    
    Call(testthis2_one)

EndProcedure


RandomAverage()

Debug "----------------------"

testthis()
Debug 3

Debug "----------------------"

testthis2(123)

Debug "----------------------"

testthis2(-1)

Debug "----------------------"

a = 12

Call(globalsub_2)

Debug "----------------------"



Sub(globalsub_1)
    Debug "In Sub globalsub_1"
EndSub

Sub(globalsub_2)
    Debug "In Sub globalsub_2"
    Debug a
EndSub

Sub names can only be used once or you get an "PureBasic - Assembler error" -> "sub_NAME: error: symbol already defined." (NAME is you sub name),
so use unique names for each sub in procedures or global subs.

There is a jump over the sub, so if you forget ProcedureReturn the code inside the sub is not called - it always jumps over the sub.

You are not allowed to call a sub from within a sub or other nesting. That's the limitation of using a global return pointer,
so only 1 sub at a time can be active.

EDIT1: Added ExitSub for jumping back immediately.
EDIT2: Changed Macro Call() for 32bit mode (removed use of EAX register).
EDIT3: renamed include to 'Sub_SingleCall.pbi'

PureBasic Forums - English

MACRO: variable evaluation ?

MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ? >> GOSUB <<

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?

Re: MACRO: variable evaluation ?