$//$ lshell.c

$//$ Your name here as a comment

#include $//$ for I$/$O functions

#include $//$ for exit$()$

#include $//$ for string functions

#include $//$ for time functions

int i$,$ j;

unsigned short temp, inst, addr;

char buf$[300]$;

FILE $*$infile;

FILE $*$outfile;

char c$,*$p$,$ letter;

unsigned short mca$[65536]$;

int mcaindex;

unsigned short start;

int gotstart;

unsigned short Gadd$[1000]$;

char $*$Gptr$[1000]$;

int Gindex;

unsigned short Eadd$[1000]$;

char $*$Eptr$[1000]$;

int Eindex;

unsigned short eadd$[1000]$;

char $*$ eptr$[1000]$;

int eindex;

unsigned short Aadd$[1000]$;

int Amodadd$[1000]$;

int Aindex;

unsigned short Vadd$[1000]$;

char $*$Vptr$[1000]$;

int Vindex;

time$\_$t timer;

int main$($int argc,char $*$argv$[])$

$\{$

if $($argc $<2)$

$\{$

printf$("$Wrong number of command line arguments

$")$;

printf$("$Usage: l $...$

$")$;

exit$(1)$;

$\}$

$//$ display your name, command line args, time

time$($&timer$)$; $//$ get time

printf$("$YOUR NAME HERE $\%$s $\%$s $\%$s$",$

argv$[0],$ argv$[1],$ asctime$($localtime$($&timer$)))$;

$//================================================================$

$//$ Step $1$:

$//$ For each module, store header entries into tables with adjusted

$//$ addresses and store machine code in mca $($the machine code array$).$

for $($i $=1$; i $<$ argc; i$++)$

$\{$

infile $=$ fopen$($argv$[$i$],"$rb$")$;

if $(!$infile$)$

$\{$

printf$("$Cannot open $\%$s

$",$ argv$[$i$])$;

exit$(1)$;

$\}$

printf$("$Linking $\%$s

$",$ argv$[$i$])$;

letter $=$ fgetc$($infile$)$;

if $($letter $!=\text{'}$o$\text{'})$

$\{$

printf$("$Not a linkable file

$")$;

exit$(1)$;

$\}$

while $(1)$

$\{$

letter $=$ fgetc$($infile$)$;

if $($letter $==\text{'}$C$\text{'})$

break;

else

if $($letter $==\text{'}$S$\text{'})$

$\{$

if $($fread$($&addr, $2,1,$ infile$)!=1)//$ addr unsigned short

$\{$

printf$("$Invalid S entry

$")$;

exit$(1)$;

$\}$

if $($gotstart$)$

$\{$

printf$("$More than one entry point

$")$;

exit$(1)$;

$\}$

gotstart $=1$; $//$ indicate S entry processed

start $=$ addr $+$ mcaindex; $//$ save adjusted address

$\}$

else

if $($letter $==\text{'}$G$\text{'})$

$\{$

if $($fread$($&addr, $2,1,$ infile$)!=1)$

$\{$

printf$("$Invalid G entry

$")$;

exit$(1)$;

$\}$

Gadd$[$Gindex$]=$ addr $+$ mcaindex; $//$ save adjusted address

j $=0$;

do $//$ get string in G entry

$\{$

letter $=$ fgetc$($infile$)$;

buf$[$j$++]=$ letter;

$\}$ while $($letter $!=\text{'}\backslash 0\text{'})$;

j $=0$;

while $($j $<$ Gindex$)//$ check for multiple definitions

$\{$

if $(!$strcmp$($buf$,$ Gptr$[$j$]))$

$\{$

printf$("$Multiple defs of global var $\%$s

$",$ buf$)$;

exit$(1)$;

$\}$

else

j$++$;

$\}$

Gptr$[$Gindex$++]=$ strdup$($buf$)$; $//$ save string

$\}$

else

if $($letter $==\text{'}$E$\text{'})$

$\{$

$//$ code missing here

$\}$

else

if $($letter $==\text{'}$e$\text{'})$

$\{$

$//$ code missing here

$\}$

else

if $($letter $==\text{'}$V$\text{'})$

$\{$

$//$ code missing here

$\}$

else

if $($letter $==\text{'}$A$\text{'})$

$\{$

$//$ code missing here

$\}$

else

$\{$

printf$("$Invalid header entry $\%$c in $\%$s

$",$ letter, argv$[$i$])$;

exit$(1)$;

$\}$

$\}$

$//$ add machine code to machine code array

while$($fread$($&inst, $2,1,$ infile$))$

$\{$

mca$[$mcaindex$++]=$ inst;

$\}$

fclose$($infile$)$;

$\}$

$//================================================================$

$//$ Step $2$: Adjust external references

$//$ handle E references

for $($i $=0$; i $<$ Eindex; i$++)$

$\{$

for $($j $=0$; j $<$ Gindex; j$++)$

if$(!$strcmp$($Eptr$[$i$],$ Gptr$[$j$]))$

break;

if $($j $>=$ Gindex$)$

$\{$

printf$("\%$s is an undefined external reference", Eptr$[$i$])$;

exit$(1)$;

$\}$

mca$[$Eadd$[$i$]]=($mca$[$Eadd$[$i$]]$ & $0$xf$800)|$

$(($mca$[$Eadd$[$i$]]+$ Gadd$[$j$]-$ Eadd$[$i$]-1)$ & $0$x$7$ff$)$;

$\}$

$//$ handle e entries

for $($i $=0$; i $<$ eindex; i$++)$

$\{$

$//$ code missing here

$\}$

$//$ handle V entries

for $($i $=0$; i $<$ Vindex; i$++)$

$\{$

$//$ code missing here

$\}$

$//================================================================$

$//$ Step $3$: Handle A entries

for $($i $=0$; i $<$ Aindex; i$++)$

$//$ Code missing here. Only $1$ statement needed to handle each A entry

$//=================================$