JAVA IMPLEMENTATION OF PASS1 of TWO PASS Assembler

An Assembler is a system software which converts an Assembly Language(ALP) into object code.A two pass assembler converts the assembly language into computer language (object code) which then passes through the linkers and loaders and then gets converted as an application file.
In the pass 1 of two pass assembler the ALP is coverted to an intermediate file which again gets converted to an object code in the pass2.

PASS1 OF A TWO PASS ASSEMBLER :

algorithm :

begin
            if starting address is given
                        LOCCTR = starting address;
            else
                        LOCCTR = 0;
            while OPCODE != END do                 ;; or EOF
                        begin
                        read a line from the code
                        if there is a label
                                    if this label is in SYMTAB, then error
                                    else insert (label, LOCCTR) into SYMTAB
                        search OPTAB for the op code
                        if found
                                    LOCCTR += N           ;; N is the length of this instruction (4 for MIPS)
                        else if this is an assembly directive
                                    update LOCCTR as directed
                        else error
                        write line to intermediate file
                        end
            PROGRAM size =  LOCCTR - starting address;
end

JAVA CODE FOR PASS 1 OF A TWO PASS ASSEMBLER:

import java.io.*;

import java.util.*;

class pass1

{

public static void main(String args[])throws Exception

{

int loc=0;

int j=0,k;

FileReader f1=new FileReader("input.txt");

BufferedReader b1=new BufferedReader(f1);

FileReader f2=new FileReader("optab.txt");

BufferedReader b2=new BufferedReader(f2);

FileWriter f3=new FileWriter("symtab.txt");

BufferedWriter b3=new BufferedWriter(f3);

FileWriter f4=new FileWriter("intermediate.txt");

BufferedWriter  b4=new BufferedWriter(f4);

StringBuffer sb = new StringBuffer();

String s,s3,s4,tmp,sd;

String s1[]=new String[3];

String s2[]=new String[3];

while((s=b1.readLine())!=null)

{
int m=0;

StringTokenizer st=new StringTokenizer(s);

while(st.hasMoreTokens())

{

s1[m]=st.nextToken();

m++;

}

if(s1[1].equals("START"))

{

b4.write("   ");

for(int h=0;h<3;h++)

{

b4.write("  ");

b4.write("  "+s1[h]);

}

loc=Integer.parseInt(s1[2]);

b4.newLine();

}

else 

{

b4.write(loc+"  ");

if(s1[0].equals("-")!=true)

{

b3.write(" "+s1[0]);

b3.write(loc+" ");

}

while((sl=b2.readLine())!=null)

{

j=0;

StringTokenizer se=new StringTokenizer(sl);

while(se.hasMoreTokens())

{

s2[j]=se.nextToken();

j++;

}

if(s1[1].equals(s2[0])==true)

loc=loc+3;

break;

}

    if(s1[1].equals("BYTE"))

loc=loc+1;

else if(s1[1].equals("RESB"))

loc=loc+(1*Integer.parseInt(s1[2]));

else if(s1[1].equals("WORD"))

loc=loc+3;

else if(s1[1].equals("RESW"))

loc=loc+(3*Integer.parseInt(s1[2]));

for(int a=0;a<3;a++)

{

b4.write("  ");

b4.write("   "+s1[a]);

}

b4.newLine();

b3.newLine();

}

}

b4.close();

b3.close();

}

}