The translation performed by an assembler is essentially a collection of substitutions:
* machine operation code for mnemonic * machine address for symbolic * machine encoding of a number for its character representation, etc. Except for one factor these substitutions could all be performed in one sequential pass over source text.The factor is the forward reference(reference to an instruction which has not yet been scanned by assembler).
Now it's that the separate passes of two pass assemblers are required to handle forward references without restriction.
Now if we impose certain restriction that means handling forward references without making two passes. These different sets of restrictions lead to one pass assembler.
And these one-pass assembler are particularly attractive when secondary storage is either slow or missing entirely, as on many small machines.
Question - Implement a single pass assembler.
Program
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
int count[20];
void main()
{
FILE *f1,*f2,*f3,*f4;
int linenumber,locctr,f;
char lbl[10],mne[10],opd[10],ch,mneu1[10],sval[10];
char sadr[10],slbl[10],op1[10],label[10];
void wordcount();
printf("Word count for Input Program:");
wordcount();
printf("\n Output \n");
printf("\n Source Code \t Object code \n\n");
f1=fopen("INPUT.C","r");
f2=fopen("SYMTAB.C","w+");
f4=fopen("INTER.C","w");
fscanf(f1,"%s %s %x\n",lbl,mne,&locctr);
linenumber=2;
while(!feof(f1))
{
if(count[linenumber]==1)
{
fscanf(f1,"%s\n",mne);
fprintf(f4,"%x\t%s",locctr,mne);
}
if(count[linenumber]==2)
{
fscanf(f1,"%s%s\n",mne,opd);
fscanf(f4,"%X \t %s \t %s \n",locctr,mne,opd);
printf("%s\t%s\t",mne,opd);
f3=fopen("OPCODE.C","r");
while(!feof(f3))
{
fscanf(f3,"%s %s \n",mneu1,op1);
if(strcmp(mne,mneu1)==0)
printf("%s\t",op1);
}
fclose(f3);
f=0;
rewind(f2);
while(!feof(f2))
{
fscanf(f2,"%s %s %s \n",sadr,slbl,sval);
if(strcmp(opd,slbl)==0)
{
printf("%s\n\n",sadr);
f=1;
}
}
if(f==0)
printf("0000\n");
}
if(count[linenumber]==3)
{
fscanf(f1,"%s %s %s \n",lbl,mne,opd);
fprintf(f4,"%X \t %s \t %s \t %s \n",locctr,lbl,mne,opd);
fprintf(f2,"%X \t %s \t %s \n", locctr, lbl,opd);
if((strcmp(mne,"RESW")==0) (strcmp(mne,"RESB")==0))
printf("%s \t %s \t 00 \t 000 %s \n\n",lbl,mne,opd);
else
printf("%s \t %s \t 00 \t 000 %s \n\n",lbl,mne,opd);
}
linenumber+=1;
if(strcmp(mne,"WORD")==0)
locctr+=3;
else if(strcmp(mne,"BYTE")==0)
locctr+=strlen(opd);
else if(strcmp(mne,"RESW)==0)
locctr+=3 * (atoi(opd));
else if(strcmp(mne,"RESB")==0)
locctr+=atoi(opd);
else
locctr+=3;
}
fclose(f1);
fclose(f2);
fclose(f4);
getch();
}
void wordcount()
{
FILE *f3;
char c;
int word=0,i=1;
printf("\n Word Count");
f3=fopen("INPUT.C","r");
c=fgetc(f3);
while(c!=EOF)
{
if(c==' ')
word+=1;
if(c=='\n')
{
word+=1;
count[i]=word;
printf("\n No.of words in %d:%d",r,word);
i+=1;
word=0;
}
c=fgetc(f3);
}
fclose(f3);
}
INPUT.c
WC START 1000
FIRST WORD 5
SECOND WORD 6
THIRD RESW 1
LDA FIRST
ADD SECOND
STA THIRD
END
OPCODE.c
LDA 00
ADD 18
SUB 1C
STA 0C
SYMTAB.c
FIRST 1009
SECOND 100C
THIRD 100F
INTER.c
1000 LDA FIRST
1003 ADD SECOND
1006 STA THIRD
1009 FIRST WORD
100C SECOND WORD
100F THIRD RESW
1012 END
1015 ENDL
1. The first problem is that the program in one pass involves forward references.
Some operands are used before they are defined and hence the assembler does not know what address to insert in the translated instruction.
2. We can list syntax errors like missing commas or parenthesis and semantic errors like duplicate definitions of symbols , other subtle errors can't be detected till pass2.
A C++ program will be able to be used for a single pass assembler program in C. This program can be used to write many different types of C++ programming.
Nothing. They are the same thing.
The output of an assembler is a part or all of a product. An assembler can work in a variety of manufacturing operations with the right training.
In order to build a two pass assembler a assembly programming language should support macro processing, file inclusion. Its definition should be independent of any particular hardware or operating system.
In the first pass of a two-pass assembler, it will "prepare" for the second pass, ie. it'll build the symbol table which is later used in the second pass to generate code.
what are the elements of assembly language programming?
FORTRAN, Assembler, to name two. Effectively, any language that allows you to reference symbols before they are declared.
Two main options for the design of assembler are: 1. One pass assembler 2. Multi-pass assembler One pass assemblers generally have problem of "forward referencing" which is resolved by using mulitpasses
pass 1 assembler is assembler which convert assembly level language into machine level language in one pass only
The output of an assembler is a part or all of a product. An assembler can work in a variety of manufacturing operations with the right training.
input file for the single pass assembler
multipass assembler means more than one pass is used by assembler.multipass assembler is used to eliminate forward references in sybol definition.it creates a number of passes that is necessary to process the definition of symbols•Multi pass assembler:-Does the work in two pass-Resolves the forward references•First pass:-Scans the code-Validates the tokens-Creates a symbol table•Second Pass:-Solves forward references-Converts the code to the machine code
Single Pass Assembler A single pass assembler scans the program only once and creates the equivalent binary program. The assembler substitute all of the symbolic instruction with machine code in one pass. AdvantagesEvery source statement needs to be processed once.DisadvantagesWe cannot use any forward reference in our program. Forward ReferenceForward reference means; reference to an instruction which has not yet been encountered by the assembler. In order to handle forward reference, the program needs to be scanned twice. In other words a two pass assembler is needed.
A two-pass assembler reads through the source code twice. Each read-through is called a pass. On pass one the assembler doesn't write any code. It builds up a table of symbolic names against values or addresses. On pass two, the assembler generates the output code, using the table to resolve symbolic names, enabling it to enter the correct values. The advantage of a two-pass assember is that it allows forward referencing in the source code because when the assembler is generating code it has already found all references.
In the first pass of a two-pass assembler, it will "prepare" for the second pass, ie. it'll build the symbol table which is later used in the second pass to generate code.
Ans: If we talk about multi-pass or say three pass assembler it afford user with lots of additional features in solving any problem for example where two pass assembler fails for example in instructions like these given below:ALFA EQU BETADELTA EQU ALFA..BETA EQU 24Where two pass assembler could only resolve forward reference upto ALFA equals BETA after getting value of BETA which is defined afterwards in the program which is forward reference but could be inefficient to allot value to DELTA simultaneously.In such conditions multi pass assembler like three pass assembler could easily resolve the issue in its third pass after getting value of ALFA in second pass and assigning it to DELTA (forward reference) in third pass.Though it could become somehow complex using this type of assembler even takes longer time too but its more reliable in programming than one or two pass assemblers which could not guarantee to solve our problem with best efficiency.
design procedure of two pass assebler
One well known and good assembler is NASM. (Netwide ASseMbler). This can be found at http://nasm.sf.net
In theory the only advantage is Speed simply because one pass is faster than two passes. However a properly written two pass assembler can be faster than a poorly written one pass assembler because the two pass assembler spends alot less time doing memory intensive lookups, look-aheads, and back-tracking.