Experiment no 3

Problem Statement:  Implementation of the Pass-I of the assembler to generate SYMTAB from   assembly language program.

Theory: Tasks performed by the Pass-I are

1. Separate the symbol table, mnemonic table, and operand fields.
2. Build the symbol table.
3. Perform LC Processing.
4. Construct Intermediate Representation (IR).

Pass-I performs the analysis of the Source Program and synthesize the IR.

Pass-I uses the following data structures:

i)                    OPTAB= A table of mnemonic opcodes and related information.

ii)                  SYMTAB= Table of Symbols used in the program.

iii)                LITTAB= A table of Literals used in the program.

iv)                POOLTAB= Table containing the information about the LITTAB.

In this experiment we will generate only the SYMTAB for the assembly language program.

SYMTAB:

• An entry in the SYMTAB contains the fields symbol, address & length.
• While processing an assembly statement if the symbol is found, the symbol & address contained in location counter LC is copied in to a new entry of SYMTAB.
• In the start of the assembly program an address is specified, this address is assigned to LC to keep track of each and every instruction.

Input: An assembly Language Program:
 

START            501

NEXT:                        MOVER         AREG,A

PRINT            ONE

A                     DS                   3

ONE                DC                  '1'

F                      EQU                200     

END

The assembly language program given above contains four symbols as NEXT, A, ONE, F.  

Input file:MEM_TAB.txt

MOVER IS (04,3)
ADD IS (01,3)
PRINT IS (10,3)
READ IS (09,3)
 

Input program: T.txt

START 501
NEXT:MOVER AREG,A
PRINT ONE
A DS 3
ONE DC '1'
F EQU 200
END

and final CPP program:

/* Symbol tabel genration*/
#include<fstream.h>
#include<iostream.h>
#include<conio.h>
#include<string.h>
#include<stdlib.h>
# define MAX 80
# define SI 30
class sym
{
char name[SI];
int add,len;
public:
void set(char [],int ,int);
void set_symbol(char []);
int msearch(char []);
int search(char []);
int get_addr(char []);
void modify(char [],int ,int);
void display();
}s;
void sym::display()
{
fstream f;
f.open("s.txt",ios::in|ios::beg);
cout<<"Symbol Tabel:-"<<endl;
while(f.read((char *)&(*this),sizeof(*this)))
{
  cout<<this->name<<" "<<this->add<<" "<<this->len<<endl;
}
f.close();
}
void sym::modify(char a[],int b,int c)
{
fstream f;
int pos,cnt=0;
f.open("s.txt",ios::out|ios::in);
while(f.read((char *)&(*this),sizeof(*this)))
{
  if(strcmp(this->name,a)==0)
  {
    pos=cnt*sizeof(*this);
    strcpy(this->name,a);
    this->add=b;
    this->len=c;
    f.seekp(pos,ios::beg);
    f.write((char *)&(*this),sizeof(*this));
  }
  else
  cnt++;
}
f.close();
}

int sym::get_addr(char a[])
{
fstream f;
f.open("s.txt",ios::in|ios::beg);
while(f.read((char *)&(*this),sizeof(*this)))
{
   if(strcmp(this->name,a)==0)
   {
    f.close();
     return (this->add);
   }
}
f.close();
return 0;
}
int sym::search(char a[])
{
fstream f;
f.open("s.txt",ios::in|ios::beg);
while(f.read((char *)&(*this),sizeof(*this)))
{
   if(strcmp(this->name,a)==0)
   {
    f.close();
     return 0;
   }
}
f.close();
return 1;
}




int sym::msearch(char a[])
{
  fstream f;
  char str[SI],str1[SI],str2[SI],strc[SI];
  f.open("mem_tab.txt",ios::in|ios::beg);
  while(f.getline(str,MAX))
  {
     strcpy(strc,str);
     strcpy(str1,strtok(str," "));
     if(strcmp(str1,a)==0)
     {
       strcpy(str,strc);
       strcpy(str1,strtok(str,","));
       strcpy(str1,strtok(NULL,","));
       strcpy(str1,strtok(str1,")"));
       f.close();
       return atoi(str1);
      }
 }
f.close();
return 0;
}
void sym::set(char a[],int b,int c)
{
fstream f;
f.open("s.txt",ios::out|ios::app);
strcpy(this->name,a);
this->add=b;
this->len=c;
f.write((char *)&(*this),sizeof(*this));
f.close();
}
void sym::set_symbol(char a[])
{
fstream f;
f.open("s.txt",ios::out|ios::app);
strcpy(this->name,a);
this->add=-1;
this->len=-1;
f.write((char *)&(*this),sizeof(*this));
f.close();
}

void main()
{
char str[SI],str1[SI],str2[SI],strc[SI],strm[SI],strv[SI];
fstream f;
int lc,flag=0,c,flag1,size,flag2;
clrscr();
f.open("t.txt",ios::beg|ios::in);
while(f.getline(str,MAX))
{
strcpy(strc,str);
if(flag==0)
{
  strcpy(str1,strtok(str," "));
  if(strcmp(str1,"START")==0)
  {
    strcpy(str1,strtok(NULL," "));
    lc=atoi(str1);
    flag=1;
  }
}
else
{
    strcpy(str,strc);
    if(strstr(str,":"))
    {
       strcpy(str1,strtok(str,":"));
       s.set(str1,lc,1);
       strcpy(strc,strtok(NULL,":"));
    }
    strcpy(str,strc);
    if(strstr(str,","))
    {
      strcpy(strm,strtok(str," "));
      strcpy(str1,strtok(NULL," "));
      strcpy(str1,strtok(str1,","));
      strcpy(str1,strtok(NULL,","));
      if(!strstr(str1,"="))
      {
        s.set_symbol(str1);
      }
     c=s.msearch(strm);
     lc=lc+c;
   }
   else
   {
       strcpy(str,strc);
       strcpy(strm,strtok(str," "));
       if(strcmp(strm,"PRINT")==0||strcmp(strm,"READ")==0)
       {
         strcpy(str1,strtok(NULL," "));
         s.set_symbol(str1);
         c=s.msearch(strm);
         lc=lc+c;
       }
      else if(strcmp(strm,"ORIGIN")==0)
      {
        strcpy(str1,strtok(NULL," "));
        flag1=s.search(str1);
        if(flag1==1)
        {
          lc=atoi(str1);
        }
        else
        {
          lc=s.get_addr(str1);
        }

     }
     strcpy(str,strc);
     strcpy(strv,strtok(str," "));
     strcpy(str1,strtok(NULL," "));
     if(strcmp(str1,"DS")==0)
     {
       strcpy(str1,strtok(NULL," "));
       size=atoi(str1);
       flag1=s.search(strv);
       if(flag1==1)
       {
         s.set(strv,lc,size);
       }
       else
       s.modify(strv,lc,size);
    lc=lc+size;
    }
    if(strcmp(str1,"DC")==0)
     {
       strcpy(str,strc);
       strcpy(str1,strtok(str,"'"));
       strcpy(str1,strtok(NULL,"'"));
       strcpy(str1,strtok(str1,"'"));
       size=atoi(str1);
       flag1=s.search(strv);
       if(flag1==1)
       {
         s.set(strv,lc,size);
       }
       else
       s.modify(strv,lc,size);
    lc++;
    }
    if(strcmp(str1,"EQU")==0)
     {

       strcpy(str1,strtok(NULL," "));
       flag2=s.search(str1);
       if(flag2==1)
       {
       size=atoi(str1);
       flag1=s.search(strv);
       if(flag1==1)
       {
         s.set(strv,size,1);
       }
       else
       s.modify(strv,size,1);
     }
     else
     {
         size=s.get_addr(str1);
       flag1=s.search(strv);
       if(flag1==1)
       {
         s.set(strv,size,1);
       }
       else
       s.modify(strv,size,1);
    }
}
}
}//else complete
if(strcmp(str,"END")==0)
break;
}//while complete
f.close();
s.display();
getch();
}