IMPLEMENTATION OF A SINGLE PASS ASSEMBLER

IMPLEMENTATION OF A SINGLE PASS ASSEMBLER

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<stdlib.h>

#define MAX 10

struct input

{

   char label[10],opcode[10],operand[10],mnemonic[5];

   int loc;

};

struct input table[MAX];

struct symtab

{

   char sym[10];

   int f,val,ref;

};

struct symtab symtb1[MAX];

void main()

{

            int f1,i=1,j=1,flag,locctr,x;

            char add[10],code[10],mnemcode[5];

            FILE *fp1,*fp2,*fp3;

            clrscr();

            printf("\nImplementation Of A Single Pass Assembler:");

            printf("\n------------------------------------------\n\n");

            fp1=fopen("input.txt","r");

            fp2=fopen("optab.txt","r");

            fp3=fopen("spout.txt","w");

            fscanf(fp1,"%s%s%s",table[i].label,table[i].opcode,table[i].operand);

            if(strcmp(table[i].opcode,"START")==0)

            {

              locctr=atoi(table[i].operand);

              i++;

              fscanf(fp1,"%s%s%s",table[i].label,table[i].opcode,table[i].operand);

            }

            else  locctr=0;

            while(strcmp(table[i].opcode,"END")!=0)

            {

              if(strcmp(table[i].label,"**")!=0)

              {

                for(x=1;x<j;x++)

                {

                  f1=0;

                  if((strcmp(symtb1[x].sym,table[i].label)==0) && (symtb1[x].f==1))

                  {

                        symtb1[x].val=locctr;

                        symtb1[x].f=0;

                        table[symtb1[x].ref].loc=locctr;

                        f1=1;  break;

                  }

                }

                if(f1==0)

                {

                  strcpy(symtb1[j].sym,table[i].label);

                  symtb1[j].val=locctr;

                  symtb1[j].f=0; j++;

                }

              }

              fscanf(fp2,"%s%s",code,mnemcode);

              while(strcmp(code,"END")!=0)

              {

                if(strcmp(table[i].opcode,code)==0)

                {

                  strcpy(table[i].mnemonic,mnemcode);

                  locctr+=3;

                  for(x=1;x<=j;x++)

                  {

                        flag=0;

                        if(strcmp(table[i].operand,symtb1[x].sym)==0)

                        {

                          flag=1;

                          if(symtb1[x].f==0)

                          table[i].loc=symtb1[x].val;

                          break;

                        }

                  }

                  if(flag!=1)

                  {

                        strcpy(symtb1[j].sym,table[i].operand);

                        symtb1[j].f=1;

                        symtb1[j].ref=i; j++;

                  }

                }

                fscanf(fp2,"%s%s",code,mnemcode);

              }

              rewind(fp2);

           

  if(strcmp(table[i].opcode,"WORD")==0)                                 

              {

                locctr+=3;

                strcpy(table[i].mnemonic,'\0');

                table[i].loc=atoi(table[i].operand);

              }

              else if(strcmp(table[i].opcode,"RESW")==0)

              {

                locctr+=(3*(atoi(table[i].operand)));

                strcpy(table[i].mnemonic,'\0');

                table[i].loc=atoi('\0');

              }

              else if(strcmp(table[i].opcode,"RESB")==0)

              {

                locctr+=(atoi(table[i].operand));

                strcpy(table[i].mnemonic,'\0');

                table[i].loc=atoi('\0');

              }

              else if(strcmp(table[i].opcode,"BYTE")==0)

              {

                ++locctr;

                if((table[i].operand[0]=='C') || (table[i].operand[0]=='X'))

                  table[i].loc=(int)table[i].operand[2];

                else

                  table[i].loc=locctr;

              }

              i++;

              fscanf(fp1,"%s%s%s",table[i].label,table[i].opcode,table[i].operand);

            }

            for(x=1;x<i;x++)

fprintf(fp3,"%s\t%s\t%s\t%s\n",table[x].label,table[x].opcode,table[x].operand,

strcat(table[x].mnemonic,itoa(table[x].loc,add,10)));

            for(x=1;x<j;x++)

              printf("%s\t%d\n",symtb1[x].sym,symtb1[x].val);

            printf("\nProgram Completed Successfully...\n");

            getch();

}

OUTPUT:

Implementation Of A Single Pass Assembler:

---------------------------------------------------------

VAR1     1009

VAR2     1012

ANS       1015

Program Completed Successfully...

INPUT FILES:

INPUT.TXT

**            START           1000

**            LDA               VAR1

**            MUL              VAR2

**            STA                ANS

VAR1     WORD           11

VAR2     WORD           12

ANS        RESW            1

**            END               **

OPTAB.TXT

START            *

ADD              18

DIV                24

LDA               00

LDCH            50

MUL              20

STA                0C

STCH             54

SUB               1C

END               *

OUTPUT FILES:

SPOUT.TXT

**               START         1000            0

**               LDA             VAR1         001009

**               MUL            VAR2         201012

**               STA              ANS            0C1015

VAR1        WORD         11                11

VAR2        WORD         12                12

ANS           RESW          1                  0