PassOne Module Implementation Specifications

Client Specifications

Implementation Data Model

Main Program calls PassOne(), for creating a Symbol table. PassOne() accomplishes the table constructions using several public functions: PassOne() calls the function GetLine(), which is in Scanner Module, to retrieve one line of characters at a time. It calls Tokenize(), which is in Scanner module, to read through the string created by GetLine() to extract labels, opcodes, operands and comments.

PassOne calls isDirective(), isComment(), isLabel() and isOpcode() to verify value of tokens encountered. When valid labels are encountered, both the name of the symbol(token) and its address are stored in a symbol table. Location counter is increased by calling addByte(), addWord() and addStr() and treated as the address of the symbol when a symbol is encountered.

searchST() is called to check symbol duplication before the symbol is inserted into symbol table. If the symbol is first time encountered, makeNode() is called to create a new SymbolNode that contains this symbol name and address, and insertSymbol() is used to add this new node into the Symbol table.

Private Importing Information

Use PassOne module needs include those information:

#include <stdio.h> - Standard C header file
#include <string.h>
#include <stdlib.h>
#include "pass.h"  - contains static records of directives, operators, special symbols, Table
structure, and all associated typedefs
#include "table.h" - contains function declarations for functions used to process tables

Private Data Type Implementations

ErrMes - ErrMes is a reference to a linked list. Each node contains a reference to character string and a reference to next node in the list. It is used to store error information about the source code during symbol table creation.

Public Data Type Implementations

SymbolTable - SymbolTable is the type named for declaring pointer to SymbolNode.

Private Function Specifications

Token Checking

int isDirective(char *str)
isDirective(str) checks whether str is a directive or not. It return true if it is a directive, false if not.
int isComment(char *string)
isComment(string) checks whether string is a comment or not. It return true if it is a comment, false if not.
int isLabel(ErrMes err, char *string)
isLabel(err, string) checks whether string is legel label or not. It return true if it is a label, false if not.
int isOpcode(ErrMes err, char *string)
isOpcode(err, string) return true if string is an opcode, false if not.

Address Value Calculating

int addByte(int lc, int n)
addByte(lc, n) returns an integer, which is equal to lc plus n.
int addWord(int lc, int n)
addWord(lc, n) returns an integer equal to (lc + n * 4).
int addStr(int lc, char *str)
addStr(lc, str) returns an integer equal to (lc + strlen(str) + 1).

Create SymbolNode

SymbolTable makeNode(char *name, int address)
makeNode(name, address) creates a new SymbolNode, and return a reference to this node.

Private Function Algorithms

isDirective
Specification

Parameter: char *str

Compare str with MIPS AL directive by using strcmp
if str is a directive
  then return an integer to indicates what kind of directive it is
  else return 0

isComment
Specification

Parameter: char *str

if str[0] = "#"
  then return true
  else return false

isLabel
Specification

Parameter: char *str
           ErrMes *err

if str is in opcode list
  then write error message into err
       return false
if there are special characters in str
  then write error message into err
       return false
if str is in symbol table list
  then write error message into err
       return false
return true

isOpcode
Specification

Parameter: char *str
           ErrMes *err

if str is in opcode list
  then return an integer to indicate what kind of opcode it is
  else write error into err
       return 0

addByte
Specification
```
Parameter: int lc, n

return lc + n
```

addWord
Specification

Parameter: int lc, n

return lc + n * 4

addStr
Specification

Parameter: int lc
           char *str

return lc + strlen(str) + 1

makeNode
Specification

Parameter: char *name
           int address

SymbolTable newNode
allocate memory space for newNode and newNode->name
strcpy(newNode->name, name)
newNode->address = address
newNode->next = NULL
return newNode

Public Function Algorithms

createST
Client Specification
```
SymbolTable sbt = NULL
return sbt
```

insertST
Client Specification

Parameter: SymbolTabel *sbt
           char *name
           int address

call makeNode(name, address) to get new SymbolTabel newNode
call searchST(sbt, name) to check duplication
if name is not in sbt
  then insert newNode into the front of sbt

searchST
Client Specification

parameter SymbolTabel sbt
          char *name

search name in sbt by using strcmp
if name is not in sbt
  then return false
  else return true

passOne
Client Specification

Parameter FILE *fp

read first input line and get toklist
initialize two location counters(one for data and one for instructions)
while not EOF and first token is not ".data" or ".text" do
  if the first token is a comment
    then read next input line
    else set error flag
if not EOF and directive = ".data"
  then if the token follow ".data" is not comment or NULL
         then set error flag
         else read next input line and get the toklist
       while not EOF and the token is not ".text" do
         if this is a legel label
           then save it and location counter in symbol table
                if next directive is ".word" or ".equ"
                  then add location counter by using addWord()
                else if it is ".byte"
                  then add location counter by using addByte()
                else if it is ".asciiz"
                  then add location counter by using addStr()
           else set error flag
         read next input line and get toklist
if not EOF and directive = ".text"
  then if the token follow ".text" is not comment or NULL
         then set error flag
         else read next input line and get the toklist
       while not EOF and the line does not begin with "__start" do
         if the line is not a comment
           then set error flag
         read next input line and get toklist
       while not EOF
         if there is a legel label
           then save it and location counter into symbol tabel
           else set error flag
         if there is an opcode
           then add location counter by 4