ASM

 
 FINISH MACRO
 mov ax, 4c00h ;call interrupt to return to DOS
 int 21h
 ENDM 
 
LOAD_DS MACRO SEG_ADDR
   MOV AX, SEG_ADDR
   MOV DS, AX
   ENDM
 
SUB_DDM MACRO X, Y, Z, Z1
   LEA AX, X
   LEA BX, Y
   LEA CX, Z
   CALL sub_dd
   ENDM
 
ADD_DDM macro X, Y, Z, Z1
SUB_DDM ZERO, Y, Z1
SUB_DDM X, Z1, Z
ENDM
 
stacksg segment para stack 'stack'
   dw 32 dup(0)
   stacksg ends
   ;
   ; 
 
datasg segment para 'data'
ZERO DD 0
Z1 DD ?
A DD 1230
B DD 100
RES DD ?
datasg ends
   ;
   codesg segment para 'code'
   test proc far
   assume ss:stacksg, ds:datasg, cs:codesg
 
   LOAD_DS datasg 
   ADD_DDM A, B, RES, Z1
   SUB_DDM B, A, RES
   SUB_DDM A, B, RES
   SUB_DDM ZERO, A, RES
   FINISH
 
test endp
   ;------------------------------------------------------------------------
   ;-------------------------------------------------------------------------
   ; sub_dd makes the following assumptions:
   ; Interface Rules:
   ; ================
   ; 1. The address of operand1 in AX; operand1 is double word
   ; 2. The address of operand2 in BX, operand2 is double word
   ; 3. The address of the result (operand1 - operand2) in CX; the difference is    stored in a double word 
   ; 4. The flags are set as required by ordinary addition in the procedure.
   ; 5. No registers including AX, BX and CX are changed.
   ; 6. 5 extra temporary words in the stack are used.
   ;
   sub_dd proc
   PUSH AX
   PUSH BX
   PUSH CX
   PUSH SI
   PUSH DI
   CLC
   MOV SI, AX ; SI points to OP1
   MOV DI, BX ; DI points to OP2
   MOV BX, CX ; BX points to OP1-OP2
   MOV AX, [SI]
   SBB AX, [DI] ;
   MOV [BX], AX ;
   INC SI
   INC SI ; address of the most significant word of OP1
   INC DI
   INC DI ; address of the most significant word of OP2
   INC BX 
   INC BX ; address of the most significant word of OP1-OP2
   MOV AX, [SI]
   SBB AX, [DI]
   MOV [BX], AX ;
   POP DI
   POP SI
   POP CX
   POP BX
   POP AX
   RET
   add_ddm A, B, RES, Z1
   sub_dd endp
 
codesg ends
   end test