Assignment

This one is fairly tough. It$$s almost like a project. For this one, you are the compiler. You need

to convert the C program given below into a MIPS program. You$$ll want to use MARS and test

the code you write to be sure it works correctly. This one problem demonstrates all of Section $9$

and is worth the entire $100$ points.

Here are the things I$$m looking for in your solution:

$$ There are no global variables other than I$/$O strings. There are a few number constants

$(-1,1,2,$ and $20)$ which can be handled with instructions that use immediate values.

$$ You should be able to do a while loop and the if$/$else constructs in assembly. I presented

them a couple of sections ago and the text details them in Section $9.$

$$ The subroutine call to fib must pass values on the stack. In fact, because it is recursive, a

stack frame must be used. See my suggested layout for the stack frame.

$$ Local variables for fib are required $($result and temp$).$ Don$$t just use registers because

recursive calls to fib will alter those registers and your code won$$t work correctly.

Again, see my suggested layout for the stack frame.

$$ If you use a register in main to hold $$number$,$ you should preserve it before calling fib

and restore it after fib returns.

$$ If you use registers in fib, you$$ll use them in recursive calls, so preserve them in the stack

frame. I suggest you use the $$T$$ registers, so you don$$t need to worry about the $$S$$

registers.

Suggested stack frame:

Pointers Usage $sp offset $fp offset

stack pointer temp $0?$

result $4?$

any registers $8-20$

original $fp $?-16$

$ra $?-12$

number $?-8$

return $?-4$

frame pointer

Depending on how many registers you use in fib, the stack frame size may vary, which is

why $sp offsets below the registers or $fp offsets above the registers cannot be

determined. Once you determine which registers you will use, you can finish the stack

frame diagram.

The C program is on the following page.

#include $//$ not necessary for the assembly; you$$ll use system calls

int fib$($int$)$; $//$ forward declaration. Again, no assembly equivalent.

void main$($void$)$

$\{$

int number $=-1$;

while $(($number $<1)||($number $>20))$

$\{$

printf$("$Enter a number $(1-20)$: $")$;

scanf$("\%$d$",$ &number$)$;

if $($number $<1)$

$\{$

printf$("$Number must be $>0,$ try again.

$")$;

$\}$

if $($number $>20)$

$\{$

printf$("$Number must be $<21,$ try again.

$")$;

$\}$

$\}$

int value $=$ fib$($number$)$;

printf$("$The fibonacci value is: $\%$d

$",$ value$)$;

$\}$

int fib$($int n$)$

$\{$

int result;

int temp;

if $($n $<2)$

$\{$

result $=$ n;

$\}$

else

$\{$

temp $=$ fib$($n$-2)$;

result $=$ fib$($n$-1)+$ temp;

$\}$

return result;

$\}$