INFO: Passing a long from C to MASM by Value & Returning a long

MORE INFORMATION

Sample Code

// Filename: CMAIN.C
// Compile options needed: /c

#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif

long MasmSub (long, long);

#ifdef __cplusplus
}
#endif

main ()
   {
   long var1 = 98304, var2 = 147456;
   printf ("%ld + %ld = %ld", var1, var2, MasmSub (var1, var2));
   }
				

Sample Code for MS-DOS Small Model Version

; Filename: MASMSUB.ASM
; Assemble options needed for MASM: /MX
; Assemble options needed for ML: /c /Cx

.MODEL small, C
.286
.CODE

MasmSub PROC, \ 
   lVar1:DWORD, \ 
   lVar2:DWORD

   mov ax, WORD PTR lVar1       ; Load the first long into DX:AX.
   mov dx, WORD PTR lVar1+2
   add ax, WORD PTR lVar2       ; Add the second long to DX:AX
   adc dx, WORD PTR lVar2+2
   ret              ; Because the function returns a long (a 4-byte
MasmSub ENDP        ; value), C will get the return value from DX:AX.
END
				

Sample Code for Windows NT Flat Model Version

; Filename: MASMSUB.ASM
; Assemble options needed for ML: /c /Cx /coff

.386
.MODEL flat, C
.CODE

MasmSub PROC, \ 
   lVar1:DWORD, \ 
   lVar2:DWORD

   mov eax, lVar1   ; Load the first long into EAX.
   add eax, lVar2   ; Add the second long to EAX.
   ret              ; Because the function returns a long (a 4-byte
MasmSub ENDP        ; value), C will get the return value from EAX.
END
				

   98304 + 147456 = 245760