Question
1
(30
marks)
The
purpose
of
this
question
is
to
write
a
complete
LC-­‐3
assembly
language
program
that
deletes
the
first
occurrence
of
a
search
string
from
within
a
source
string.
The
program
must
consist
of
a
main
program
and
the
subroutines
described
below.
You
must
follow
standard
programing
practices
and
establish
a
stack
and
pass
arguments
and
return
values
via
the
stack.
Each
subroutine
must
establish
a
frame
pointer
and
access
parameters
and
the
return
value
via
the
frame
pointer.
That
is,
ALL
communication
between
routines
must
use
the
stack.
Each
subroutine
must
save
and
restore
any
registers
it
uses
using
the
stack.
Consider
the
C
header:
void
readText(char
*stringPtr,
int
stringSize,
char
*prompt)
Write
an
LC-­‐3
assembly
language
subroutine
named
readText
that
is
given
the
address
at
which
a
string
is
to
be
stored
(stringPtr),
the
maximum
number
of
characters
that
may
be
stored
in
the
string
(stringSize)
and
the
address
of
a
prompt
to
display
to
the
user
(prompt).
Display
the
prompt
to
the
user.
In
a
loop
read
characters
from
the
keyboard
and
insert
the
characters
into
the
string
until
either
the
return/enter
key
is
pressed
or
the
string
is
full.
Be
sure
that
the
last
character
in
the
string
is
the
null
character
0.
Suppose
stringSize
is
32
and
32
characters
are
read
from
the
keyboard.
The
character
at
position
32
must
be
overwritten
with
0
to
ensure
the
string
ends
with
a
0.
COMP
2280
Assignment
3
Page
2
of
5
As
this
subroutine
does
i/o
you
must
save
and
restore
R7.
Consider
the
C
header:
int
findText(char
*source,
char
*search)
Write
an
LC-­‐3
assembly
language
subroutine
named
findText
that
is
given
the
address
of
a
zero
terminated
source
string
(source)
and
the
address
of
a
zero
terminated
search
string
(search).
This
subroutine
must
return
the
position
of
the
first
occurrence
of
the
string
search
within
the
string
source.
The
position
of
the
first
character
in
source
is
1.
If
the
string
search
is
not
found
within
the
string
source
return
-­‐1.
Consider
the
C
header:
int
lengthStr(char
*text)
Write
an
LC-­‐3
assembly
language
subroutine
named
lengthStr
that
is
given
the
address
of
a
zero
terminated
string
(text)
and
returns
the
number
of
characters
in
text.
The
zero
at
the
end
of
the
string
is
not
included
in
the
number
of
characters
in
the
string.
Consider
the
C
header:
void
delete(char
*source,
int
position,
int
length)
Write
an
LC-­‐3
assembly
language
subroutine
named
delete
that
is
given
the
address
of
a
zero
terminated
string
(source),
the
position
(position)
of
the
first
character
to
delete
from
source,
and
the
number
of
characters
to
delete
(length)
from
source.
The
position
of
the
first
character
in
source
is
1.
Delete
the
specified
characters
from
source.
The
main
program
must
include
the
following
assembler
directives.
stackbase .fill xFD00
eop .stringz "\n\nProgrammed by Stew Dent.\nEnd of
processing.\n"
position .blkw 1
length .blkw 1
searchMsg .stringz "\nEnter the search string: "
searchLen .fill 32
search .blkw 32
resultMsg .stringz "\nThe source string is:\n"
sourceMsg .stringz "\nEnter the source string: "
sourceLen .fill 128
source .blkw 128
COMP
2280
Assignment
3
Page
3
of
5
The
main
program
must
do
the
following:
• Establish
the
stack
pointer
• Call
readText
to
read
in
the
source
string
• Call
readText
to
read
in
the
search
string
• Call
findText
to
get
the
position
of
the
search
string
within
the
source
string
• Save
the
position
of
the
search
string
within
the
source
string
at
the
memory
location
labeled
position
• Call
lengthStr
to
get
the
length
of
the
search
string
• Save
the
length
of
the
search
string
at
the
memory
location
labeled
length
• Call
delete
to
delete
the
search
string
from
the
source
string
• Display
resultMsg
• Display
the
value
of
source
(the
value
of
the
source
string
after
the
search
string
has
been
deleted)
• Display
the
end
of
processing
message
that
contains
your
name
(not
Stew
Dent)
You
will
have
to
modify
the
algorithm
for
the
main
program
given
above
so
that
if
findText
returns
a
negative
value
lengthStr
and
delete
are
not
called.
A
sample
run
of
the
program
is
shown
below.
Enter the source string: jjejeljelljello
Enter the search string: jell
The source string is:
jjejeljello
Programmed by Stew Dent.
End of Processing.
You
should
also
test
your
program
with
the
following
values:
Source:
123456789
Search:
123
Result:
456789
Source:
123456789
Search:
6789
Result:
12345
Source:
123456789
Search:
XXX
Result:
123456789