To practice writing assembly and passing parameters, you will implement the math functions of a calculator.

The add.S and sub.S files will be trivial to complete, but mul.S and divd.S will take some careful planning. You must either repeatedly add or repeatedly subtract $($and count$)$ the first input number by the second. mod.S might be trivial, but pow.S will be challenging.

When finished the calculator should be able to add $+,$ subtract $-,$ multiply $*,$ divide $/,$ modulo $\%$ and power $^.$

Here is an example session:

$>2+3$

$5$

$>5-1$

$4$

$>1-5$

$-4$

$>-3+2$

$-1$

$>6/3$

$2$

$>7/3$

$2$

$>5/3$

$1$

$>-5/3$

$-1$

$>-6/-3$

$2$

$>-6*-3$

$18$

$>6*3$

$18$

$>-6*3$

$-18$

$>3^2$

$9$

$>2^4$

$16$

$>7\%3$

$1$

$>6/0$

$0$

You should strive to complete this functionality in as few instructions as possible.

Only write your solution in the provided assembly files $($inside the func$/$ directory$).$

Use repeated addition to calculate the result of multiplication. You will need to construct a loop yourself!

Use repeated subtraction to calculate the quotient. Again, you will need to construct a loop yourself!

Do not simply generate assembly using the compiler and submit it$.$ I will know.

Only worry about negative numbers for add $+,$ subtract $-,$ multiply $*$ and divide $/.$

Parameter Passing

Parameters are passed to functions in the registers r$15,$ r$14,$ r$13$ and r$12$ in that order $($something special happens if there are more than $4$ arguments to a function$).$ The functions you are implementing are receiving the first number $($left of operator$)$ in r$15$ and the second number $($right of operator$)$ in r$14.$ Remember, when the microcontroller executes the ret instruction at the end of a function, the return value should be in r$15!$

Assembly Instructions

Here are some useful instructions you might need:

mov src$,$ dst ; move the contents of src to dst

sub src$,$ dst ; subtract the value in src from dst and store the result in dst

add src$,$ dst ; add the value in src to the value in dst and store the result in dst

clr dst ; zero out destination $($same as mov #$0,$ dst$)$

cmp a$,$ b ; make the comparison: b $[<,>=,==,!=]$ a

jl label ; jump to label if b $<$ a

jge label ; jump to label if b $>=$ a

jeq label ; jump to label if b $==$ a

jne label ; jump to label if b $!=$ a

jn label ; jump to label if N is set $($result of previous instruction was negative$)$

jmp label ; jump to label unconditionally $($always$)$

A more complete listing can be found on page $56$ of the Family User's Guide.

Registers

You can use any of the registers r$4-$ r$15,$ however do not use registers r$0-$ r$3$ for anything in your function. These registers serve special purposes on the MSP$430.$

Callee$-$Saved Registers

Furthermore, a called function is required to preserve the callee$-$saved registers $($r$4-$ r$10)$ so that they have the same value on return from a function as they had at the point of the call.

All other general$-$purpose registers are caller$-$save; that is$,$ they are not preserved across a call, so if thier value is needed following the call, the caller is responsible for saving and restoring their contents. For example:

int main$()\{$

printf$("$Hello$,$ World

$")$;

return $0$;

$\}$