Q61590: Passing a long* from a C Module to an Assembly Module

Article: Q61590
Product(s): Microsoft Macro Assembler
Version(s): 5.1,5.1a,6.0,6.0a,6.0b
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 5.1, 5.1a, 6.0, 6.0a, 6.0b 
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SUMMARY
=======

The following code demonstrates passing a LONG INT (4 bytes) via a far pointer
(4 bytes) to an assembly routine that accesses the LONG integer.

Each integer is incremented in the assembly routine and its new value returned to
the calling C program.

MORE INFORMATION
================

Sample Code
-----------

  /* Compile options needed: /AL
  */ 

  #include <stdio.h>
  #include <process.h>
  #include <conio.h>

  extern void IncLongs( long *, long * );

  void main()
  {
     long *n1,*n2;               /* 4 byte pointers  */ 

     long int t1 = 9999999L;     /* 4 byte variables */ 
     long int t2 = 2256789L;

     n1 = &t1;
     n2 = &t2;

     /* initial values */ 
     printf( "The values are  %ld and  %ld\n ", *n1, *n2 );

     printf( "Incrementing values...\n" );
     IncLongs( n1, n2 );

     /* values returned by the assembly routine */ 
     printf( "The values are  %ld and  %ld\n ", *n1, *n2 );
  }

  ========================================================

  ; Assemble options needed: none

           .model large, c
           .data
           .code
  IncLongs PROC far arg1:dword, arg2:dword
           PUSH es                 ; save registers
           PUSH si
           LES si,arg1             ; load in es:si the seg:offset of n1
           INC word ptr es:[si]
           JNC doarg2
           INC word ptr es:[si+2]  ; if carry, increment high word of n1

  doarg2:
           LES si,arg2             ; load in es:si the seg:offset of n2
           INC word ptr es:[si]
           JNC finis
           INC word ptr es:[si+2]  ; if carry, increment high word of n2

  finis:
           POP si                  ; restore registers
           POP es
           MOV sp,bp
           RET
  IncLongs ENDP

           END

Additional query words: 5.10 5.10a 6.00 6.00a 6.00b

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM600a kbMASM510a kbMASM600b
Version           : :5.1,5.1a,6.0,6.0a,6.0b

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