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Dec 2nd, 2008
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using STDCALL

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My homework assignment is to convert this c++ code into assembly. Here is the code
Assembly Syntax (Toggle Plain Text)
  1. void maxInt (int xVal, int yVal, int& big)
  2. {
  3.      big = xVal;
  4.      if ( big < yVal )
  5.           big = yVal;
  6.      return;
  7. }
I have successfully created a program that will find the larger integer and return it, but we have to use the STDCALL technique. I am not real sure on how to do that. Would I push xVal, yVal, and big on the stack, then call maxInt? The code I have now just stores the entered integers in xVal and yVal and uses eax to do all my cmp's and everything and I don't push or pop anything on the stack. Here is my code. I use the Irvine routine that came with my book but everything is pretty self explanitory if you aren't familiar with these. Any help or pointers would be greatly appreciated.
Assembly Syntax (Toggle Plain Text)
  1. INCLUDE Irvine32.inc
  2. .data
  3.  
  4. xVal		DWORD	?
  5. yVal		DWORD	?
  6.  
  7. Message BYTE "Enter each integer on sepatate line. Enter -9999 for both to quit.",0dh,0ah,0
  8. MessageE BYTE "Integers are equal.",0
  9. MessageB BYTE "The larger integer was: ",0
  10.  
  11. .code
  12. main PROC
  13. 	mov	 edx,OFFSET Message
  14. 	call WriteString
  15. 	call	ReadInt				; Enter first integer
  16. 	mov	xVal,eax				; Stores the first value in xVal
  17. 	call	ReadInt				; Enter second integer
  18. 	mov	yVal,eax				; Stores the second value in yVal
  19. 	call	maxInt				; Calls the maxInt PROC
  20. 	call crlf					; Carriage return line feed
  21. 	call main					; Goes back to main
  22.  
  23. main ENDP
  24.  
  25. ;---------------------------------------------------------------
  26. maxInt PROC
  27. ;
  28. ; Calculates and returns the larger of the two integers entered by
  29. ; the user.
  30. ;
  31. ; Receives:	xVal, yVal, the two integers
  32. ; Returns:	eax
  33. ;---------------------------------------------------------------
  34.  
  35. 	mov	eax,xVal				; Moves xVal to eax
  36. 	cmp	yVal,eax				; Compares yVal to eax
  37. 	je	L1					; Jumps to L1 if equal
  38. 	jg	L3					; Jumps to L3 if eax > yVal
  39. 	jl	L4					; Jumps to L4 if eax < yVal
  40.  
  41. L1:	cmp	eax,-9999				; Compares -9999 to eax
  42. 	jne	L2					; Jumps to L2 if eax does not equal -9999
  43. 	exit						; Exits program if eax equals -9999
  44.  
  45. L2:	mov	 edx,OFFSET MessageE
  46. 	call	WriteString
  47. 	ret						; Returns back to main
  48.  
  49. L3:	mov eax,yVal				; Moves the larger integer(yVal) to eax
  50. 	jmp L4					; Jumps to L4
  51.  
  52. L4:	mov	 edx,OFFSET MessageB
  53. 	call WriteString
  54. 	call	WriteInt				; Displays the larger integer
  55. 	ret						; Returns back to main
  56.  
  57. maxInt ENDP					; Ends maxInt PROC
  58.  
  59. END main
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Dec 4th, 2008
1

Re: using STDCALL

;Hi.
;Actually why did you compare eax with -9999 ?
cmp eax,-9999 ;?
----------------------------------------------------------------
;stdcall is pushing on the stack values in the opposite order:
push val2
push val1
call myfunc
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Dec 6th, 2008
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Re: using STDCALL

Entering -9999 for both ends the program. Ok, I think I understand whats goin on now. I'll try that and see what happens.
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Dec 7th, 2008
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Re: using STDCALL

Not to be nit-picky, but void really don't have a "return".
And since maxInt never really had an input, perhaps there should
be two functions since maxInt just checks the comparisons.

Assembly Syntax (Toggle Plain Text)
  1. bool maxInt(int, int, int&)
  2. {
  3.     ...return true if x and y have a diffrence...
  4. }
  5.  
  6. void printInt(int x, int y, int big)
  7. {
  8.     if(x == -9999) { ...set kill signal... }
  9.  
  10.     bool difference = maxInt(x, y, big);
  11.     if(!diffrence) { cout << "They were the same" << endl; }
  12.     else
  13.     {
  14.        cout << "Big is: " << big << endl;
  15.     }
  16. }

I suppose it doesn't matter if you have it all in one function or not. Personal preference in design.
Last edited by MosaicFuneral; Dec 7th, 2008 at 3:52 am.
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Dec 8th, 2008
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Re: using STDCALL

Is the right? I'm using the push and everything. I'm still not using all the variable though(xVal, yVal, and &big). How would I incorporate those into my program?
Assembly Syntax (Toggle Plain Text)
  1. INCLUDE Irvine32.inc
  2. .data
  3.  
  4. xVal	DWORD	?
  5. yVal	DWORD	?
  6. big	DWORD	?
  7.  
  8. Message BYTE "Enter each integer on sepatate line. Enter -9999 for both to quit.",0dh,0ah,0
  9. MessageE BYTE "Integers are equal.",0
  10. MessageB BYTE "The larger integer was: ",0
  11.  
  12. .code
  13. main PROC
  14. 	mov	edx,OFFSET Message
  15. 	call WriteString
  16. 	call	ReadInt				; Enter first integer
  17. 	mov	xVal,eax				
  18. 	call	ReadInt				; Enter second integer
  19. 	mov	yVal,eax
  20. 	push yVal
  21. 	push xVal
  22. 	call	maxInt				; Calls the maxInt PROC
  23. 	call crlf					; Carriage return line feed
  24. 	call main					; Goes back to main
  25.  
  26. main ENDP
  27.  
  28. ;---------------------------------------------------------------
  29. maxInt PROC
  30. ;
  31. ; Calculates and returns the larger of the two integers entered by
  32. ; the user.
  33. ;
  34. ; Receives:	xVal, yVal, the two integers
  35. ; Returns:	eax
  36. ;---------------------------------------------------------------
  37.  
  38. 	push	ebp
  39. 	mov	ebp,esp				; Base of stack frame
  40. 	mov	eax,[ebp + 12]			; second integer
  41. 	mov	yVal,eax
  42. 	mov	eax,[ebp + 8]			; first integer
  43. 	cmp	yVal,eax
  44. 	jg	L1
  45. 	jl	L5
  46. 	je	L3
  47.  
  48. L1:	mov	eax,yVal
  49. 	jmp	L5
  50.  
  51. L3:	cmp	eax,-9999
  52. 	jne	L4
  53. 	exit
  54.  
  55. L4:	mov	edx,OFFSET messageE
  56. 	call	WriteString
  57. 	pop	ebp
  58. 	ret	8
  59.  
  60. L5:	mov	edx,OFFSET messageB
  61. 	call WriteString
  62. 	call	WriteInt
  63. 	pop	ebp
  64. 	ret	8
  65.  
  66. maxInt ENDP					; Ends maxInt PROC
  67.  
  68. END main
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Dec 8th, 2008
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Re: using STDCALL

Assembly Syntax (Toggle Plain Text)
  1. INCLUDE Irvine32.inc
  2. maxInt proto xVal:DWORD, yVal:DWORD
  3. ;.....................
  4. push 2 ; yVal
  5. push 3 ; xVal
  6. call maxInt
  7. ;.....................
  8. maxInt proc xVal:DWORD, yVal:DWORD
  9.      mov eax, xVal
  10.      cmp eax, yVal
  11.      jl lbl1
  12.      jg lbl2
  13.      cmp eax, -9999
  14.      jne lbl3
  15.      ;exit
  16.      lbl3:
  17.      ;they are equal
  18.      ;exit
  19.      lbl1:
  20.      ;yVal more
  21.      ;exit
  22.      lbl2:
  23.      ;xVal more
  24.      ;exit
  25. maxInt endp
;didnt try must work.
Last edited by low_coder; Dec 8th, 2008 at 5:04 pm.
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Re: using STDCALL

Assembly Syntax (Toggle Plain Text)
  1. INCLUDE Irvine32.inc
  2. maxInt proto xVal:DWORD, yVal:DWORD
  3. ;.....................
  4. push 2 ; yVal
  5. push 3 ; xVal
  6. call maxInt
  7. ;.....................
  8. maxInt proc xVal:DWORD, yVal:DWORD
  9.      mov eax, xVal
  10.      cmp eax, yVal
  11.      jl lbl1
  12.      jg lbl2
  13.      cmp eax, -9999
  14.      jne lbl3
  15.      ;exit
  16.      lbl3:
  17.      ;they are equal
  18.      ;exit
  19.      lbl1:
  20.      ;yVal more
  21.      ;exit
  22.      lbl2:
  23.      ;xVal more
  24.      ;exit
  25. maxInt endp
;didnt try must work.
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