Program to Subtract Two 32 Bit Numbers

May 4, 2011 by ProjectsGeek Leave a Comment

Objective

Write a Program to Subtract Two 32 Bit Numbers in Assembly language.

Algorithm for Subtract Two 32 Bit Numbers

We have 32 bit numbers. Initially we will load the first 32 bit number into the registers AX and BX.
AX contains the LSB while BX contains the MSB of the number.
Loading is done using the MOV instruction.
Now we will load the second 32 bit number into the registers CX and DX. CX contains the LSB and DX contains the MSB of the number.
Initially, we will subtract the LSBs i.e. to subtract the contents of CX with contents of AX. The subtraction is done using SUB instruction.
The result of LSB subtraction is stored in AX.
Now, we will subtract the MSB alongwith borrow if any generated in the LSB subtraction i.e. we are subtracting DX from BX using SBB (subtract with borrow) instruction.
The result of MSB subtraction is in register BX.
Display the result using display routine.

For example :	BX : AX = 12345678 H		12345678 H
	DX : CX = 11111111 H	–	11111111 H
			01234567 H

Algorithm to Subtract Two 32 Bit Numbers

Step I      : Initialize the data segment.
Step II     : Load the LSB of first number into AX register.
Step III   : Load the MSB of first number into BX register.
Step IV    : Load the LSB of the second number into CX register.
Step V     : Load the MSB of the second number into DX register.
Step VI    : Subtract the two LSBs.
Step VII   : Subtract the two MSBs along with borrow.
Step VIII : Display the result.
Step IX     : Stop.

Program to Subtract Two 32 Bit Numbers 1

Program to Subtract Two 32 Bit Numbers

.model small  
 .data  
 op1 dd 12345678h                                                         
 op2 dd 11111111h  
 ans dd ?  
 .code  
      mov      ax, @data  
      mov      ds, ax  
      mov      ax, word ptr op1          ; lsb of number1 in ax  
      mov      bx, word ptr op1+2        ; msb of number1 in bx   
      mov      cx, word ptr op2          ; lsb of number2 in cx  
      mov      dx, word ptr op2+2        ; msb of number1 in dx  
      sub      ax, cx                    ; subtract lsb + lsb  
      mov      word ptr ans, ax          ; lsb answer  
      mov      word ptr ans+2, bx        ; msb answer  
      mov      bx, word ptr ans+2        ; Result in reg bx  
      mov      dh, 2  
 l1:     mov      ch, 04h                ; Count of digits to be displayed  
      mov      cl, 04h                   ; Count to roll by 4 bits  
 l2:     rol      bx, cl                 ; roll bl so that msb comes to lsb   
      mov      dl, bl                    ; load dl with data to be displayed  
      and      dl, 0fH                   ; get only lsb  
      cmp      dl, 09                    ; check if digit is 0-9 or letter A-F  
      jbe      l4  
      add      dl, 07                    ; if letter add 37H else only add 30H  
 l4:     add      dl, 30H  
      mov      ah, 02                    ; INT 21H (Display character)  
      int      21H  
      dec      ch                        ; Decrement Count  
      jnz      l2  
      dec      dh  
      cmp      dh, 0  
      mov      bx, word ptr ans          ; display lsb of answer  
      jnz      l1  
      mov      ah, 4ch                   ; Terminate Program  
      int      21h  
 end

How to Run this Program

For Running this program you should have installed Tasm on you computer . If you have not installed Tasm yet please install from Here .

For more project on assembly language programs or codes.

C:\programs>tasm 32sub.asm
Turbo Assembler  Version 3.0  Copyright (c) 1988, 1991 Borland International
Assembling file:   32sub.asm
Error messages:    None
Warning messages:  None
Passes:            1
Remaining memory:  437k
C:\programs>tlink 32sub
Turbo Link  Version 3.0 Copyright (c) 1987, 1990 Borland International
Warning: No stack
C:\programs>32sub
01234567

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