Passing a long* from a C Module to an Assembly Module
ID: Q61590
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The information in this article applies to:
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Microsoft Macro Assembler for MS-DOS, versions 5.1, 5.1a, 6.0, 6.0a, 6.0b
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
Keywords :
Version : :5.1,5.1a,6.0,6.0a,6.0b
Platform :
Issue type :